Photochemistry: Volume 49

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Photochemistry of transition metal complexes (2019–2020)

  • Published: 20 Sep 2021
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V. Dichiarante, A. Strada, and G. Bergamaschi, in Photochemistry: Volume 49, ed. S. Crespi and S. Protti, The Royal Society of Chemistry, 2021, vol. 49, pp. 177-211.

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This Chapter aims to summarise the major advances achieved over 2019 and 2020 in the field of photochemistry and photocatalysis by transition metal compounds. In the last years, one of the central research themes has been the development of efficient photocatalytic complexes based on earth-abundant metals as a potential eco-friendly, resource-efficient, and sustainable photochemical approach. Nevertheless, second- and third-row metal complexes still represent key building blocks in the design of new photocatalysts in organic transformations, biomedical applications, as well as in green chemistry fields.

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Mining the right transition metals in a vast chemical space

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Swift and significant gains against climate change require the creation of novel, environmentally benign, and energy-efficient materials. One of the richest veins researchers hope to tap in creating such useful compounds is a vast chemical space where molecular combinations that offer remarkable optical, conductive, magnetic, and heat transfer properties await discovery.

But finding these new materials has been slow going.

“While computational modeling has enabled us to discover and predict properties of new materials much faster than experimentation, these models aren’t always trustworthy,” says Heather J. Kulik  PhD ’09, associate professor in the departments of Chemical Engineering and Chemistry. “In order to accelerate computational discovery of materials, we need better methods for removing uncertainty and making our predictions more accurate.”

A team from Kulik’s lab set out to address these challenges with a team including Chenru Duan PhD ’22.

A tool for building trust

Kulik and her group focus on transition metal complexes, molecules comprised of metals found in the middle of the periodic table that are surrounded by organic ligands. These complexes can be extremely reactive, which gives them a central role in catalyzing natural and industrial processes. By altering the organic and metal components in these molecules, scientists can generate materials with properties that can improve such applications as artificial photosynthesis, solar energy absorption and storage, higher efficiency OLEDS (organic light emitting diodes), and device miniaturization.

“Characterizing these complexes and discovering new materials currently happens slowly, often driven by a researcher’s intuition,” says Kulik. “And the process involves trade-offs: You might find a material that has good light-emitting properties, but the metal at the center may be something like iridium, which is exceedingly rare and toxic.”

Researchers attempting to identify nontoxic, earth-abundant transition metal complexes with useful properties tend to pursue a limited set of features, with only modest assurance that they are on the right track. “People continue to iterate on a particular ligand, and get stuck in local areas of opportunity, rather than conduct large-scale discovery,” says Kulik.

To address these screening inefficiencies, Kulik’s team developed a new approach — a machine-learning based “recommender” that lets researchers know the optimal model for pursuing their search. Their description of this tool was the subject of a paper in Nature Computational Science in December.

“This method outperforms all prior approaches and can tell people when to use methods and when they’ll be trustworthy,” says Kulik.

The team, led by Duan, began by investigating ways to improve the conventional screening approach, density functional theory (DFT), which is based on computational quantum mechanics. He built a machine learning platform to determine how accurate density functional models were in predicting structure and behavior of transition metal molecules.

“This tool learned which density functionals were the most reliable for specific material complexes,” says Kulik. “We verified this by testing the tool against materials it had never encountered before, where it in fact chose the most accurate density functionals for predicting the material’s property.”

A critical breakthrough for the team was its decision to use the electron density — a fundamental quantum mechanical property of atoms — as a machine learning input. This unique identifier, as well as the use of a neural network model to carry out the mapping, creates a powerful and efficient aide for researchers who want to determine whether they are using the appropriate density functional for characterizing their target transition metal complex. “A calculation that would take days or weeks, which makes computational screening nearly infeasible, can instead take only hours to produce a trustworthy result.”

Kulik has incorporated this tool into molSimplify, an open source code on the lab’s website, enabling researchers anywhere in the world to predict properties and model transition metal complexes.

Optimizing for multiple properties

In a related research thrust, which they showcased in a recent publication in JACS Au , Kulik’s group demonstrated an approach for quickly homing in on transition metal complexes with specific properties in a large chemical space.

Their work springboarded off a 2021 paper showing that agreement about the properties of a target molecule among a group of different density functionals significantly reduced the uncertainty of a model’s predictions.

Kulik’s team exploited this insight by demonstrating, in a first, multi-objective optimization. In their study, they successfully identified molecules that were easy to synthesize, featuring significant light-absorbing properties, using earth-abundant metals. They searched 32 million candidate materials, one of the largest spaces ever searched for this application. “We took apart complexes that are already in known, experimentally synthesized materials, and we recombined them in new ways, which allowed us to maintain some synthetic realism,” says Kulik.

After collecting DFT results on 100 compounds in this giant chemical domain, the group trained machine learning models to make predictions on the entire 32 million-compound space, with an eye to achieving their specific design goals. They repeated this process generation after generation to winnow out compounds with the explicit properties they wanted.

“In the end we found nine of the most promising compounds, and discovered that the specific compounds we picked through machine learning contained pieces (ligands) that had been experimentally synthesized for other applications requiring optical properties, ones with favorable light absorption spectra,” says Kulik.

Applications with impact

While Kulik’s overarching goal involves overcoming limitations in computational modeling, her lab is taking full advantage of its own tools to streamline the discovery and design of new, potentially impactful materials.

In one notable example, “We are actively working on the optimization of metal–organic frameworks for the direct conversion of methane to methanol,” says Kulik. “This is a holy grail reaction that folks have wanted to catalyze for decades, but have been unable to do efficiently.” 

The possibility of a fast path for transforming a very potent greenhouse gas into a liquid that is easily transported and could be used as a fuel or a value-added chemical holds great appeal for Kulik. “It represents one of those needle-in-a-haystack challenges that multi-objective optimization and screening of millions of candidate catalysts is well-positioned to solve, an outstanding challenge that’s been around for so long.”

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  • Published: 24 February 2021

Synthesis, characterization, and biological studies of some biometal complexes

  • Vinay Kumar Srivastava 1  

Future Journal of Pharmaceutical Sciences volume  7 , Article number:  51 ( 2021 ) Cite this article

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Metal complexes Cu[C 13 H 8 O 4 N] 2 2, Ni[C l3 H 8 O 4 N] 2 3, and Co[C 13 H 8 O 4 N] 2 4 of bioinorganic relevance have been synthesized with the Schiff base ligand 2-furylglyoxal–anthranilic acid (FGAA) [C 13 H 9 O 4 N] 1 .

All the complexes are well characterized by various spectral and physical methods. The antimicrobial activity of the complexes has been studied against some of the pathogenic bacteria and fungi.

Results indicate that complexes have higher antimicrobial activity than the free ligand. This would suggest that chelation reduces considerably the polarity of the metal ions in the complexes which in turn increases the hydrophobic character of the chelate and thus enables permeation, through the lipid layer of microorganisms. All the complexes were assessed for their anticancer studies against a panel of selected cancer cells HOP62 and BT474 respectively. Results showed that the complexes are promising chemotherapeutic alternatives in the search of anticancer agents. The fluorescence quenching phenomenon is observed in the Schiff base metal complexes.

The octahedral transition metal complexes 2, 3, and 4 have been obtained by treatment of ligand 2-furylglyoxal-anthranilic acid (FGAA) 1 with metal acetate. Complexes under investigations have shown antimicrobial, potential anticancer, and the DNA binding studies.

Graphical abstract

research on transition metal complexes

The chemistry of transition metal complexes has received considerable attention largely due to their catalytic and bioinorganic relevance. Such complexes are also important due to their potential biological activities such as antibacterial, antifungal, antimalarial, and antitumor [ 1 , 2 , 3 , 4 ]. Medicinal inorganic chemistry is comparatively a new discipline which developed after the serendipitous discovery of the antitumor activity of cisplatin [ 5 , 6 , 7 ]. The clinical success of this platinum complex has stimulated considerable interest in the search for new metal complexes as modern therapeutics, diagnostic, and radiopharmaceutical agents. Copper, nickel, and cobalt complexes are used in the treatment of many diseases including cancer and as potential hypoxia-activated prodrugs [ 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. Coordination compounds which form coordinate bonds via the sulfur, oxygen, and nitrogen donor atoms are well known and have a long history. The interest in preparation of new metal complexes gained the tendency of studying the interactions of metal complexes with DNA for their applications in biotechnology and medicine.

Deoxyribonucleic acid (DNA) is the primary target molecule for most anticancer and antiviral therapies according to cell biologists. Investigation on the interaction of DNA with small molecules is important in the design of new type of pharmaceutical molecule. Schiff base constitutes an important class of nitrogen donor ligands and occupy a prominent position among the recent achievement in the field of coordination chemistry. The azomethine which is the functional group of Schiff base is aided in forming a stable complex. The chemistry of Schiff base metal complexes is exploited in industries, technologies, and in medicinal fields. The present investigations deal with the synthesis, characterization, antimicrobial, anticancer, and DNA cleavage studies of Cu(II), Ni(II), and Co(II) metal complexes containing Schiff base ligand 2-furylglyoxal-anthranilic acid (FGAA).

All reagents used were of analytical grade and used as purchased commercially; however, the solvents were purified by the standard procedure [ 15 ]. The ligand 2-furylglyoxal-anthranilic acid (FGAA) was prepared by the reported procedure [ 16 , 17 , 18 , 19 , 20 ]. C, H, and N were analyzed on Carlo-Erba microanalyzer. Metal contents were estimated by standard procedure [ 21 ]. FTIR was recorded on Thermo Nicolet Avater 370. Electronic spectra on Shimadzu UV-160A spectrophotometer. The conductance measurements were carried out on a metal CM-180 Eliodigital conductivity meter. Magnetic studies were done by a Guoy balance using Hg [Co (SCN) 4 ] as the calibrant.

1 H and 13 C NMR spectra in dimethyl sulfoxide (DMSO) were recorded on a Brucker WH 300 (200 MHz) and Varian Gemini (200 MHz) spectrometers using tetramethylsilane (TMS) as an internal reference.

The in vitro antimicrobial screening effects of the investigated compounds were tested against the bacterial species: Escherichia coli , ( E. coli ) and Klbsiella pneumoniae ( K. pneumoniae ), and fungal species: Aspergillus niger ( A. niger ) and Candida albicans ( C. albicans ) by using Kirby Bauer Disk diffusion method [ 22 , 23 , 24 ]. Chloramphenicol and nystatin were used as the standard antibacterial and antifungal agents. The tested compounds were dissolved in DMF solution (which has no inhibition activity) and solution soaked in filter paper disk of 5 mm diameter and 1 mm thickness. The disks were incubated 24 h for bacterial and 72 h for fungal species at 37 °C. The minimum inhibitory concentration (MIC) value of the compounds was determined by the serial dilution method [ 25 , 26 , 27 ].

The in vitro cancer studies of all the compounds were assessed for their anti-proliferation test against a panel of selected human cancer cell lines such as HOP62 (lung) and BT 474 (breast) by using SRB (sulforhodamine B) assay [ 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ] concentration of drug used 10, 20, 40, and 80 μg/mL ADR (adrimycin) was used as a positive control which controls cells with definite structure and clear cell wall without degeneration. Each drug was assayed inducing 50% growth inhibition (GI 50 ), total growth inhibition (TGI), and 50% cytotoxicity (LC 50 ) after a 48 h incubation period were calculated by linear interpolation from the observed data points. Fluorescence measurements were recorded on an F-7000 FL spectrophotometer at room temperature.

Synthesis of metal complexes (2-4)

Metal complexes of Cu[C 13 H 8 O 4 N) 2 2, Ni [C 13 H 8 O 4 N] 2 3 , and Co [C 13 H 8 O 4 N] 2 4, were synthesized by the addition of ethanolic solution of ligand 2-furylglyoxal–anthranilic acid 1 (2 mmol) copper acetate/nickel acetate/cobalt acetate (1 mmol). The mixture was magnetically stirred and refluxed for 2 h. The complexes obtained were filtered, washed with ethanol, and dried.

All the metal complexes were colored, non-hygroscopic in nature, and stable at room temp. They were insoluble in common organic solvents but soluble in DMF and DMSO. The results of the elemental analysis are in good agreement with the calculated values. The molar conductance value indicates their non-electrolytic nature. Physical and analytical data of complexes are summarized in Table  1 .

On the basis of analytical and spectral data, octahedral geometry has been assigned to the complexes. The results of antimicrobial activity and anticancer studies indicate metal complexes are much more active as compared to ligand fragments. Fluorescence quenching phenomena are observed in its metal complexes by fluorescence studies.

IR spectral studies

Infrared spectra of free ligand, a sharp band [ 38 , 39 , 40 ] appeared at 1615-1590 cm –1 ascribed to the stretching vibrations of azomethine group and was shifted to lower frequency region after complexation suggesting thereby the participation of imine nitrogen. A strong band appeared at 1735-1690 cm –1 in the IR spectra of ligand (FGAA) which is due to the presence of stretching vibration of carbonyl group coordination through this carbonyl oxygen to the central metal ion is confirmed by a negative shift in this frequency in the spectra of corresponding metal complexes. IR spectra of ligand displays a bond of medium intensity in the region of 3550-3490 cm –1 due to the –OH stretching vibration of free –CO 2 H group. Coordination of ligand as a consequence of deprotonation of – CO 2 H group is evident by the disappearance of the above band in the IR spectra of respective complexes [ 41 , 42 ]. Furthermore, the asymmetrical and symmetrical vibrations of COO – group appeared at 1560-1535 cm –1 and 1340-1325 cm –1 Δν (as–s) value 220-210 cm –1 further indicate the coordination through unidentate carboxylate group. Some new bands appeared in the IR spectra of metal complexes at 550-530 cm –1 , 450-430 cm –1 , and 335-325 cm –1 are probably due to the formation of M–O, M–N, and M–S bonds respectively which further give additional evidences in favor of the coordination of metals through azomethine nitrogen, carbonyl oxygen, and carboxylate group.

Electronic spectral and magnetic studies

Divalent copper having a d 9 configuration give rise to a 2D free ion term which split into a regular octahedral environment into a lower doublet 2 E g and an upper triplet 2 T 2g levels. In electronic spectra [ 43 , 44 , 45 , 46 ] of a true octahedral system, only one band due to 2 E g → 2 T 2g transitions is expected but true octahedral structures are not common. Therefore, instead of a one broad band due to 2 E g → 2 T 2g transition. These transitions from the ground state 2 B 1g → 2 A 1g → 2 B 2g and 2 E g are expected as a consequence of John-Tellers configuration stability. The 2 E g orbitals separate so that one goes up as much as the other goes down.

The T 2g orbitals separate in such a way that the doubly degenerate pair goes down only half as far as the single orbital goes up therefore in case of Cu (II); there is no net energy change for T 2g electrons since four are stabilized while two are destabilized due to which Cu(II) complex shows distortion in an octahedral geometry. The electronic spectra of Cu(II) complex displays three spectral bands in the region 10635, 14850, 16345 cm –1 which are in good agreement with the distorted geometry of complex under investigation. This geometry is further supported by the magnetic moment value 1.98 B.M. of the complex. In the Ni(II) complex, three bands in the range 10750, 1665, 25650 cm –1 corresponding to the transition 3 A 2g → 3 T 2g → 3 T 1g and 3 T 1g (P) are observed which clearly indicate the octahedral geometry. The theoretical value of ν 2 /ν 1 for octahedral Ni(II) complex is found 1.55. The observed value lies 1.60 which is in conformity with the distorted octahedral geometry of the ligand around central Ni(II) ion lowering the ratio of ν 2 /ν 1 may be attributed due to configuration interaction between T 1g (P) and T 1g (F) excited state. The octahedral geometry is further supported by their magnetic value 3.14 B.M. In octahedrally surrounded Co(II) ions, three bands in the region 8000, 15616, 18175 cm –1 are expected which may be assigned to 4 T 1g to 4 T 2g (F) (ν 1 ), 4 A 2g (F) (ν 2 ), and 4 T 1g (P) (ν 3 ) transitions respectively. The 4 A 2g transition is very weak and often appears as shoulder. Cobalt complex possesses an octahedral geometry which is further confirmed by the energy ratio ν 2 /ν 1 lies 1.95 and magnetic moment value 4.60 B.M.

NMR spectral studies

In the 1 H NMR spectra of free Schiff base ligand, the signals were appeared in the range of 7.15-7.20 ppm due to (HC=N) proton [ 47 ]. However, in the spectra of Schiff base metal complexes of Cu(II), Ni(II), and Co(II), the signals were observed in the downfield regions of 8.0–9.0 ppm supporting the coordination of iminonitrogen atom to Cu (II)/Ni (II)/Co (II) [ 48 ] while the free ligand NMR spectra has a characteristic NMR signal for carboxyl group proton in the 10.5-12.5 ppm range, the disappearance of this signal in the 1 H NMR spectra of metal complexes indicating the involvement of carboxylate ion oxygen in chelation through deprotonation. There is no appreciable change in the peak position corresponding to NH and aromatic protons. The 13 C–NMR signals for the metal, complexes are assigned by the comparison with the spectra of corresponding free Schiff base ligand. A downfield shift of CH = N group in the range of 150-160 ppm and for 175-182.5 ppm. In the complexes, NMR spectra indicate that the ligand coordinates through both the nitrogen atom of CH = N and the oxygen of COO — ion [ 49 , 50 , 51 , 52 ] (Fig.  1 ).

figure 1

The proposed structure of metal complex M = Cu(II) or Ni(II) or Co(II)

In vitro antimicrobial studies

The antibacterial and antifungal activity of the ligand and complexes [ 53 , 54 ] were assayed against some of the bacteria and fungi. DMF is used as negative control and chloramphenicol is used as a positive standard for antibacterial and nystatin for antifungal activities (Fig.  2 a and b). The minimum inhibitory concentration (MIC) value of the compounds was determined by the serial dilution method and is given in Table  2 .

figure 2

a Antibacterial studies of ligand and its metal complex against E. coli and K. pneumoniae . b Antifungal studies of ligand and its metal complex against A. niger and C. albicans

The in vitro antimicrobial activity results revealed that complexes are more microbial toxic than the ligand. The activity order of the synthesized complexes and ligand are as follows 2 > 4 > 3 > 1 .

Such increased activity of the metal chelates can be explained on the basis of Tweedy’s chelation theory on chelation, the polarity of the metal ion will be reduced to a greater extent due to the overlap of the ligand orbital and partial sharing of the positive charge of the metal ion with donor groups. Further, it increases the delocalization of π electrons over the whole chelate ring and enhances the penetration of the metal complexes into lipid membranes and blocking of the metal-binding sites in the enzymes of microogranism. These complexes also disturb the respiration process of the cell and thus block the synthesis of proteins which restricts further growth of the organism. The complex 2 shows higher antimicrobial activity than other complex 3 and 4 complex. The variation in the effectiveness of different compounds against different organisms depends either on the impermeability of the cells of the microbes or on differences in ribosome of microbial cells. Further, lipophilicity which controls the rate of entry of molecules into the cells is modified by coordination so compounds 2 , 3 , and 4 can become more active than compound 1 compared to the standard compounds chloramphenicol and nystatin (Fig.  2 a and b); the present metal complexes are much less active against the representative strains of microorganism [ 55 , 56 ].

In vitro anticancer studies

The data obtained by the SRB assay show that metal complexes 2 and 3 have inhibitory effects on the growth of HOP62 (Tables  3 and 4 ) (Fig.  3 ) and BT474 (Tables  5 and 6 ) (Fig.  4 ). Cancer cells in dose-dependent manner. Complex 4 exhibits cytotoxic effect on BT474 cancer cells but no antiproliferative effect against cell line HOP62. The antiproliferative effect of tested complexes is likely due to the lipophilicity of the complexes that alleviate the transport of metal complexes into the cell and posteriorly into the organelles where metal may possibly contribute to toxicity by inhibitory cellular respiration and metabolism of biomolecules [ 57 , 58 , 59 ]. The pure metals are inactive however the activity of metal cations varies on their bioavailability hence delivery methods/solubility and ionization of metal sources are significant parameters to deal metals in biological system [ 60 , 61 , 62 ] possibly this is the reason that bonding of metal cations (Cu(II)/Ni(II)/Co(II) to biologically compatible ligand (FGAA) enhances the bioavailability and ultimately the activity of metal cations. In contrast, coordination enhances the activity of the metal complexes against BT 474 and HOP 62 cell lines. The compound 1 (ligand) exhibited no cytotoxic effect on both the cell lines. The choice of the coordinated ligand (s) seems to be as important as the choice of metal(s) because besides being the integral part of biologically active complexes. These organic molecules (ligands) can exert a biological activity of their own. The photomicrograph of the cells treated with compounds 1, 2, 3, and 4 revealed the morphological features of apoptosis consist of membrane blebbing, nuclear condensation, cytoplasmic shrinkage, DNA fragmentation, cell wall destruction, and formation of apoptotic bodies (Figs.  5 and 6 ). Morphological images were grabbed using a phase-contrast microscope at × 20 magnifications with a digital camera at 48 h after treatment with the samples. Compound 1 showed negligible cytotoxicity as the cell growth and morphology did not get affected whereas it can be seen clearly that the compounds 2 , 3 , and 4 affected the normal morphology which rendered the cells to lose their viability. The picture revealed that the cells treated with compounds 2 , 3 , and 4 exhibited apoptotic cellular death as the population of cells reduced drastically within the 48 h of treatment. The photomicrograph depicts the treatment of HOP 62 and BT 474 cells treated with complexes 2 , 3 , and 4 showed a significant inhibitory effect on the cellular growth. In all two cell lines, the increase in the number of cells with abnormal morphology was accompanied by an increase in the number of irregular refractive clumps. The majority of the cell appear to be rounded and shrunken due to apoptosis and white spots in the images showing the apoptotic cell. The percentage cell viability in presence of ligand and metal complexes for BT 474 and HOP 62 cell lines are shown in Figs.  3 and 4 . The graphs of percentage control growth versus molar drug concentration showed the effective drug concentration on both cell lines and each point is the mean standard error obtained from three independent experiments. The results showed that complexes 2 , 3 , and 4 were the most potent and strongly inhibited the proliferations of both the two cell lines in a dose-dependent manner with TGI values 17.3, 30.3, and 46.4 μg/ml respectively. It was verified that the increased in concentration of complexes leads to higher cytotoxic activities. Nevertheless, results also proved that ADR showed superior cytotoxic activity against both cell lines.

figure 3

Growth curve: human lung cancer cell line HOP 62 compounds 1-4

figure 4

Growth curve: human breast cancer cell line BT 474 compounds 1 - 4

figure 5

HOP 62 Cell images compounds 1 - 4

figure 6

BT474 Cell images compounds 1-4

Fluorescence studies

Emission intensity of the three complexes increases on increasing the conc. of CT DNA. The enhancement of emission intensity is an indication of binding for the complexes to the hydrophobic pockets of DNA and complexes can be protected efficiently by the hydrophobic environment inside the DNA helix [ 63 , 64 ]. The high binding affinities of the metal complexes are probably attributed to the extension of the π system of the intercalated ligand due to the co-ordination of transition metal ions which also leads to a planar area greater than that of the free ligand and the coordinated ligand penetrating more deeply into and stacking more strongly with base pairs of DNA. The quenching plots illustrate that the quenching of ethidium bromide (EtBr) bound to DNA by the complexes are in good agreement with the linear Stern-Volmer equation which proves that the three complexes bind to DNA. The K b (slope/intercept values in graph of F 0 / F vs (conc.) values for complexes 2 , 3 , and 4 are 2.225 × 10 2 M –1 , 1.94 × 10 2 M –1 , and 1.55 × 10 2 M –1 ). Based on the K b values, the order of binding strength of metal complexes 2 > 3 > 4 (Figs.  7 , 8 , 9 ).

figure 7

a Fluorescence quenching curves of ethidium bromide bound to DNA in presence of Ni (II) complex. b Stern-Volmer plots of the fluorescence titration for Ni (II) complex. Representation of slope and Intercept values. Kb = slope/Intercept value i.e. 1.94 × 10 2 M -1 F0 = Highest emission of DNA+Etbr, F = Highest emission of DNA+Etbr after addition of complexes

figure 8

a Fluorescence quenching curves of ethidium bromide bound to DNA in presence of Cu (II) Complex. b Stern-Volmer plots of the fluorescence titrations for Cu (II) Complex. Representation of slope and intercept values. Kb = slope/Intercept value i.e. 2.225 × 10 2 M -1

figure 9

a Fluorescence quenching curves of ethidium bromide bound to DNA in presence of Co (II) complex. b Stern-Volmer plots of the fluorescence titrations for Co (II) Complex. Representation of slope and intercept values. Kb = slope/Intercept value i.e. 1.55 × 10 2 M -1

Conclusions

In the present study, novel metal complexes of Cu(II), Ni(II), and Co(II) were prepared and characterized by physico-chemical methods. Spectral studies demonstrate the ligand coordinating through azomethine nitrogen and carboxylate oxygen atoms and reveal octahedral geometry for Cu(II), Ni(II), and Co(II) complexes. The antibacterial and antifungal data given for the compound presented in this paper allowed us to state that the metal complexes generally have better activity than the ligands and less activity than standards. The metal complexes exerted growth inhibition on the human tumor cell lines showing promise as potential anticancer drugs deserving of further investigation. The Schiff base exhibits a strong fluorescence emission contrast to this partial fluorescence quenching phenomena is observed in its metal complexes.

Availability of data and materials

Available on request

Abbreviations

2-Furylglyoxal-anthranilic acid

Tera methyl silane

Dimethyl formamide

Dimethyl sulfoxide

Minimum inhibitory concentration

Sulforhodamine B

50% growth inhibition

Total growth inhibition

Cytotoxic killing of 50% of cells

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Acknowledgements

The author express his gratitude to the STIC, Cochin University, CDRI, Lucknow , S.P Centre for Science and Technology Vallabh Vidhya Nagar, and ACTREC Mumbai for providing facilities of spectral and biological studies.

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Srivastava, V.K. Synthesis, characterization, and biological studies of some biometal complexes. Futur J Pharm Sci 7 , 51 (2021). https://doi.org/10.1186/s43094-021-00191-w

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  • Metal complexes
  • Characterization
  • Antimicrobial
  • Anticancer activity
  • DNA binding

research on transition metal complexes

Experimental and theoretical insight of Schiff base transition metal complexes: synthesis, characterization, antimicrobial and COVID-19 molecular docking studies

  • Published: 24 November 2023
  • Volume 50 , pages 413–436, ( 2024 )

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  • Indu Sindhu 1 &
  • Anshul Singh 1  

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In the current research work, a series of Co(II), Cu(II), Ni(II) and Zn(II) complexes of novel 5,5′-[(1-E,1′-E)-(4-nitro-1,2-phenylene)bis(azaneylylidene)bis(methaneylylidene) bis(2 methoxy phenol)] (NAMM) Schiff base ligand have been synthesized by the condensation reaction of 4-nitro-o-phenylenediammine with 3-hydroxy-4-methoxy-benzaldehyde. The characterization study of Schiff base ligand and its metal complexes is executed by various instrumental and spectral techniques such as 1 H-nuclear magnetic resonance, 13 C-nuclear magnetic resonance, infrared spectroscopy, mass analysis, ultraviolet–visible technique, elemental analysis, electron paramagnetic resonance, thermogravimetric analysis and powder X-ray diffraction techniques to know information about the structures of compounds. The spectral data reveal the hexadentate nature of synthesized metal complexes. To clarify the conductive and optical properties of complexes, direct optical energy band gap and Urbach spectral tail energy were estimated. The thermodynamic and kinetic parameters were calculated by Coats–Redfern method. In addition, the docking was carried out with two different proteins, COVID-19 main protease (PDB-6LU7) and human prostate specific antigen in a fab sandwich (PDB-3QUM) and the results revealed a large negative binding affinity value for zinc complex for both receptors, thereby exhibiting good protein–complex interactions. Further, the compounds were in silico screened for their biocompatibilities and pharmacokinetic behavior through ADMET and PASS studies which signifies the drug-like character of the synthesized compounds. Moreover, antimicrobial studies were evaluated against four different bacterial strains as well as two fungal strains and results evinced highest activity of copper complex (2) against E. coli (MIC-0.0055 μmol/mL) and C. albicans (MIC-0.0110 μmol/mL).

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Acknowledgements

The authors highly acknowledge SAIF, IIT Bombay, for providing (ESR JEOL) analytical facility.

This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors.

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Department of Chemistry, Baba Mastnath University, Asthal Bohar, Rohtak, 124021, India

Indu Sindhu & Anshul Singh

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IS was involved in data curation, writing—original draft preparation, investigation, visualization. AS helped in conceptualization, methodology, project administration, validation, writing—review and editing, supervision.

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Sindhu, I., Singh, A. Experimental and theoretical insight of Schiff base transition metal complexes: synthesis, characterization, antimicrobial and COVID-19 molecular docking studies. Res Chem Intermed 50 , 413–436 (2024). https://doi.org/10.1007/s11164-023-05179-0

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  • Published: 07 March 2024

Atomically engineering metal vacancies in monolayer transition metal dichalcogenides

  • Xiaocang Han 1   na1 ,
  • Mengmeng Niu 2   na1 ,
  • Yan Luo 3   na1 ,
  • Runlai Li   ORCID: orcid.org/0000-0002-1857-2037 4 ,
  • Jiadong Dan 5 ,
  • Yanhui Hong 6 ,
  • Alex V. Trukhanov 7 ,
  • Wei Ji   ORCID: orcid.org/0000-0001-5249-6624 8 ,
  • Yeliang Wang 2 ,
  • Jiahuan Zhou 9 ,
  • Jingsi Qiao 2 ,
  • Jin Zhang   ORCID: orcid.org/0000-0003-3731-8859 1 &
  • Xiaoxu Zhao   ORCID: orcid.org/0000-0001-9746-3770 1 , 10  

Nature Synthesis ( 2024 ) Cite this article

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Scanning probe microscopy and scanning transmission electron microscopy (STEM) are powerful tools to trigger atomic-scale motions, pattern atomic defects and lead to anomalous quantum phenomena in functional materials. However, these techniques have primarily manipulated surface atoms or atoms located at the beam exit plane, leaving buried atoms, which govern exotic quantum phenomena, largely unaffected. Here we propose an electron-beam-triggered chemical etching approach to engineer shielded metal atoms sandwiched between chalcogen layers in monolayer transition metal dichalcogenide (TMDC). Various metal vacancies \(({{{\mathrm{V}}}}_{{{\rm{MX}}}_{{n}}},\,{n}=0{-}6)\) have been fabricated via atomically focused electron beam in STEM. The parent TMDC surface was modified with surfactants, facilitating the ejection of sandwiched metal vacancies via charge transfer effect. In situ sequential STEM imaging corroborated that a combined chemical-induced knock-on effect and chalcogen vacancy-assisted metal diffusion process result in atom-by-atom vacancy formation. This approach is validated in 16 different TMDCs. The presence of metal vacancies strongly modified their magnetic and electronic properties, correlated with the unpaired chalcogen p and metal d electrons surrounding vacancies and adjacent distortions. These findings show a generic approach for engineering interior metal atoms with atomic precision, creating opportunities to exploit quantum phenomena at the atomic scale.

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Acknowledgements

X.Z. thanks the Fundamental Research Funds for the Central Universities, the National Natural Science Foundation of China (grant no.52273279), the Beijing Natural Science Foundation (no. Z220020) and the open research fund of Songshan Lake Materials Laboratory (grant no. 2023SLABFN26). J.Q. thanks Ministry of Science and Technology (MOST) of China (grant no. 2018YFE0202700), the National Natural Science Foundation of China (grant nos. 11974422, 12204534 and 62171035) and the Strategic Priority Research Program of the Chinese Academy of Sciences (grant no. XDB30000000). The authors acknowledge the Electron Microscopy Laboratory of Peking University, China for the use of Cs-corrected Nion U-HERMES200 scanning transmission electron microscopy.

Author information

These authors contributed equally: Xiaocang Han, Mengmeng Niu, Yan Luo.

Authors and Affiliations

School of Materials Science and Engineering, Peking University, Beijing, China

Xiaocang Han, Jin Zhang & Xiaoxu Zhao

MIIT Key Laboratory for Low-Dimensional Quantum Structure and Devices & Advanced Research Institute of Multidisciplinary Science, Beijing Institute of Technology, Beijing, China

Mengmeng Niu, Xu Wu, Yeliang Wang & Jingsi Qiao

Frontiers Science Center for Flexible Electronics and Institute of Flexible Electronics, Northwestern Polytechnical University, Xi’an, China

College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, China

NUS Centre for Bioimaging Sciences, National University of Singapore, Singapore, Singapore

Jiadong Dan

DP Technology, Beijing, China

Yanhui Hong

SSPA ‘Scientific and Practical Materials Research Centre of NAS of Belarus’, Minsk, Belarus

Alex V. Trukhanov

Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-Nano Devices, Department of Physics, Renmin University of China, Beijing, China

Wangxuan Institute of Computer Technology, Peking University, Beijing, China

Jiahuan Zhou

AI for Science Institute, Beijing, China

Xiaoxu Zhao

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Contributions

X.Z. and J. Zhang conceived and designed the experiments. X.H. and Y.L. synthesized materials and performed the STEM characterizations. M.N. and J.Q. built the theoretical model and performed DFT calculations. X.H., M.N. and Y.L. conducted all analysis under the supervision of J.Q., J. Zhang and X.Z. R.L., J.D., X.W., A.V.T., W.J., Y.W. and J. Zhou contributed to the sample measurements and mechanism understanding. Y.H. conducted deep deep-learning experiment. X.H., M.N., J.Q. and X.Z. co-wrote the manuscript. All the authors discussed the results and contributed to preparing the manuscript.

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Correspondence to Jingsi Qiao , Jin Zhang or Xiaoxu Zhao .

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Nature Synthesis thanks Marijn van Huis and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary handling editor: Alexandra Groves, in collaboration with the Nature Synthesis team.

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Spin density and structures of metal vacancy in TMDCs.

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Han, X., Niu, M., Luo, Y. et al. Atomically engineering metal vacancies in monolayer transition metal dichalcogenides. Nat. Synth (2024). https://doi.org/10.1038/s44160-024-00501-z

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Organic Synthesis via Transition Metal-Catalysis

In recent years, the development of transition-metal-catalyzed reactions has acquired an increasing importance. In fact, the use of transition metal complexes as catalysts may allow performing important organic transformations in one synthetic step by the assembly of simple units under sustainable conditions [ 1 ]. This Special Issue reports significant contributions in this field. In particular, seven papers have been published: two reviews and five original research articles.

The first review (by Garazi Urgoitia, Maria Teresa Herrero, Fátima Churruca, Nerea Conde, and Raul SanMartin) reports on the use of palladium pincer complexes as catalysts or pre-catalysts for the direct arylation of arenes with aryl halides or pseudo-halides [ 2 ]. This is a particularly important process, which allows aryl–aryl coupling (also intramolecularly) using an arene (or heteroarene) as one coupling partner, with C–H activation.

The second review (by Mieko Arisawa and Masahiko Yamaguchi) concerns the synthesis of a plethora of organosulfur compounds by rhodium-catalyzed S–S bond cleavage of disulfides or elemental sulfur and subsequent transfer of the ensuing organothio groups to organic substrates [ 3 ].

In the first original research article, Jérémy Ternel, Adrien Lopes, Mathieu Sauthier, Clothilde Buffe, Vincent Wiatz, Hervé Bricout, Sébastien Tilloy, and Eric Monflier describe the reductive hydroformylation (performed under 80 bar pressure of a 1:1 CO/H 2 mixture, in toluene at 80 °C) of isosorbide diallyl ether (readily available by allylation of bio-sourced isosorbide). The process is catalyzed by a rhodium/amine catalytic system, [typically, Rh(acac)(CO) 2 /Et 3 N], to give the corresponding high value-added bis-primary alcohols [ 4 ].

The second original research article (by Joanna Palion-Gazda, André Luz, Luis R. Raposo, Katarzyna Choroba, Jacek E. Nycz, Alina Bieńko, Agnieszka Lewińska, Karol Erfurt, Pedro V. Baptista, Barbara Machura, Alexandra R. Fernandes, Lidia S. Shul’pina, Nikolay S. Ikonnikov, and Georgiy B. Shul’pin) reports on the use of methyl-substituted 8-hydroxyquinolines (Hquin) for the preparation of five-coordinated oxovanadium(IV) complexes [VO(2,6-(Me) 2 -quin) 2 , VO(2,5-(Me) 2 -quin) 2 , and VO(2-Me-quin) 2 ]. These complexes were then used as catalysts for the efficient oxidation of hydrocarbons (to alcohols) and alcohols (to ketones), carried out with H 2 O 2 in acetonitrile at 50 °C in the presence of 2-pyrazinecarboxylic acid (PCA) as a cocatalyst [ 5 ].

The subsequent papers report on transition-metal-promoted cyclization processes leading to heterocyclic derivatives. Thus, new polycyclic heterocycles (1 H -benzo[4,5]imidazo[1,2- c ][1,3]oxazin-1-ones) were synthesized by Lucia Veltri, Roberta Amuso, Marzia Petrilli, Corrado Cuocci, Maria A. Chiacchio, Paola Vitale, and Bartolo Gabriele using a ZnCl 2 -promoted deprotective annulation approach starting from N -Boc-2-alkynylbenzimidazoles under mild conditions (CH 2 Cl 2 as the solvent at 40 °C for 3 h) [ 6 ]. N -benzoylindoles were obtained by Zhe Chang, Tong Ma, Yu Zhang, Zheng Dong, Heng Zhao, and Depeng Zhao by Pd(II)-catalyzed oxidative C–H functionalization and annulation of substituted N -(2-allylphenyl)benzamides, carried out with Pd(OAc) 2 as the catalyst in the presence of benzoquinone as the oxidant and dibutyl phosphate as the additive in DMSO at 60–70 °C [ 7 ]. An annulative C–H activation process was also developed by Bao Wang, Xu Han, Jian Li, Chunpu Li, and Hong Liu for the synthesis of fused isochromeno-1,2-benzothiazine derivatives, starting from S -phenylsulfoximides and 4-diazoisochroman-3-imine. The process, catalyzed by [Cp*RhCl 2 ] 2 in the presence of AgOPiv, takes place in trifluoroethanol at room temperature under air [ 8 ].

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2.1.1: Introduction to transition metal complexes (coordination complexes)

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Transition metals are found in the middle of the periodic table. In addition to being found in the metallic state, they also form a range of compounds with different properties. Many of these compounds are ionic or network solids, but there are also some molecular compounds, in which different atoms are arranged around a metal ion. These compounds are called transition metal complexes or coordination complexes . They are often brightly-colored compounds and they sometimes play very useful roles as catalysts or even as pharmaceuticals.

Because of their relatively low electronegativity, transition metals are frequently found as positively-charged ions, or cations. These metal ions are not found by themselves, instead, they attract other ions or molecules to themselves. These species bind to the metal ions, forming coordination complexes.

Hexaamminecobalt(III) chloride, [Co(NH 3 ) 6 ]Cl 3 , is an example of a coordination complex. It is a yellow compound. The "complex" part refers to the fact that the compound has a bunch of different pieces. There is a cationic part, which itself is a moderately complicated structure, plus three chloride anions.

Cobalt with six NH3 groups bound to it, overall charge of +3. Three chlorine counterions are associated.

Potassium hexachloroplatinate, K 2 [PtCl 6 ], is another good example. It is another bright yellow compound. This time, the anion is the more complex part, and there are two potassium ions as well.

Platinum with six chlorine atoms bound to it, overall charge of -2. Two potassium counterions are associated.

The formulae for coordination complexes always give you hints about the structures. The stuff inside the square brackets always makes up one of the ions. In that part, there are a number of things attached to the transition metal. Those things attached to the transition metal are called ligands; we'll take a closer look at them later. The part outside the square brackets tells you what the counterions are; those are there to balance out the charge of the ion inside the square brackets.

Very often, the counterions are individual atomic ions, like chloride anions (Cl - ) or potassium cations (K + ). So, when you see the K 2 within the formula, the potassium atoms are not connected together; they are two separate potassium ions: 2 K + . Likewise, the Cl 3 at the end of a formula does not really mean a group of three chlorine atoms clustered together; they are three separate chloride ions, 3 x Cl - .

Sometimes, polyatomic ions that act as counterions to these complexes; this is especially common in the case of anions. Most often, they are oxoanions, in which an atom has some number of oxygens attached to it. A couple of the most common examples are nitrate (NO 3 - ) and sulfate (SO 4 2- ); these ions have been known for hundreds of years. Tetrafluoroborate (BF 4 - ) and hexafluorophosphate (PF 6 - ) are a couple of twentieth-century anions.

A number of common ions are listed in the table below. Most of them have a +1 or -1 charge. Sulfate is the only common example listed with a 2- charge.

Monoatomic anions: bromide, chloride, and iodide. Monoatomic cations: lithium, sodium, potassium. Polyatomic anions: sulfate, nitrate, perchlorate, chlorate, tetrafluoroborate, hexafluorophosphate.

Note that some of these structures use a charge-minimised Lewis structure. In third-row elements, these structures may contain additional bonds to the central atom, going past the octet, in order to lower the number of + and - charges. Sulfate and perchlorate can also be drawn as octet-obedient structures, in which the sulfur and chlorine have true octets, and charge separation occurs. However, hexafluorophosphate has no octet-obedient Lewis structure; regardless of how you draw it, the phosphorus has six bonds.

Exercise \(\PageIndex{1}\)

Draw the octet-obedient structures for (a) sulfate and (b) perchlorate.

Sulfate anion with two negatively-charged oxygens and two double bonded neutral oxygens. This resonates to a form with a +2 charge on sulfur and -1 charges on all oxygens, all single bonds.

Exercise \(\PageIndex{2}\)

Indicate the individual ions in the following complexes.

  • [Co(NH 3 ) 4 Cl 2 ]Cl
  • [Co(NH 3 ) 5 Cl]Cl 2
  • [Co(NH 3 ) 5 NO 2 ]Cl 2
  • [Co(NH 3 ) 5 OH 2 ]Cl 3
  • K 2 [PtCl 4 ]
  • Na 2 [Co(SCN) 4 ]
  • [Pt(NH 3 ) 2 (OH 2 ) 2 ](NO 3 ) 2
  • [Co(NH 3 ) 4 (OH 2 ) 2 ] 2 (SO 4 ) 3

Cobalt complex ion with two chlorines bonded and four amino groups, overall charge of +3. Three chloride counterions.

We haven't drawn proper Lewis structures for these coordination complexes so far. For the hexachloroplatinate complex, the Lewis structure is shown below:

Platinum complex ion with six chlorine groups, overall charge of -2. Two potassium counterions.

The electron accounting looks like this:

Two electrons for each bond takes up 12 electrons. That leaves 42 more. If each chlorine gets three lone pairs, that uses up another 36 electrons. There are six left, and they could be left on the platinum.

That is a lot of electrons. But remember where platinum sits in the periodic table: it's a transition metal. How many electrons does the next noble gas have? Eighteen: that's radon. This structure works out perfectly in terms of reaching a noble gas configuration.

For another example, let's take a look at the cobalt complex.

Cobalt complex ion with six amino groups, overall charge of +3. Three chloride counterions.

This time, the electron counting looks like:

A dozen of those electrons get used for the six Co-N bonds, leaving 42 more. We need another 36 for the eighteen N-H bonds; that leaves six electrons. We can just put those on the cobalt, like last time.

Each nitrogen ends up with its octet (eight electrons in four bonds). Each hydrogen has its "octet" (two electrons in a bond, corresponding to helium's noble gas configuration. Cobalt also gets its "octet" (eighteen electrons corresponding to krypton's noble gas configuration).

These are still really big, unwieldy numbers. We need a simplification. We won't really count up all of the electrons in coordination complexes because they tend to be assembled from pre-existing parts (the "ligands") that already have their octets. The ligands are just donating their electrons to the metal in the center. Instead, we focus on that metal, and see how many electrons it has once all of the ligands have been attached.

Also, notice that in the Lewis structure of the cobalt complex, we neglected the formal charges. That's actually common practice with transition metal complexes. The reason for that is simply that the structure is getting pretty crowded with all the lone pairs and formal charges. Normally, in order to simplify an already complicated structure, the lone pairs on the transition metal and the formal charges are not shown.

Cobalt complex ion with six protonated amino groups, overall charge of +3. Three chloride counterions.

On the next page, we will practice electron counting some more. We will also take a look at some common ligands: the pieces that are directly attached to the transition metal ions.

See a more in-depth discussion of coordination complexes in a later course.

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COMMENTS

  1. Computational Discovery of Transition-metal Complexes: From High

    Transition-metal complexes are attractive targets for the design of catalysts and functional materials. The behavior of the metal-organic bond, while very tunable for achieving target properties, is challenging to predict and necessitates searching a wide and complex space to identify needles in haystacks for target applications. This review will focus on the techniques that make high ...

  2. Learning properties of metal complexes

    Research Highlight; Published: 20 April 2023; Transition metal complexes. Learning properties of metal complexes. Kaitlin McCardle 1 Nature Computational Science volume 3, page 281 (2023)Cite this ...

  3. Recent Advance in Transition Metal Complexes and Their Applications

    This Special Issue presents the latest research on transition-metal complexes and their applications, including characterization and property studies on structurally interesting metal complexes, applications of metal complexes in various transformation reactions and mechanistic studies. Dr. Yungen Liu. Guest Editor.

  4. A hexagonal planar transition-metal complex

    Abstract. Transition-metal complexes are widely used in the physical and biological sciences. They have essential roles in catalysis, synthesis, materials science, photophysics and bioinorganic ...

  5. Charge-transfer processes in metal complexes enable ...

    Apart from polypyridine complexes of second-row transition metals such as Ru ii (refs 7,17,23,28), there has also been long-standing interest in complexes of third-row metals such as Ir iii (refs ...

  6. Active Learning Exploration of Transition-Metal Complexes to Discover

    Transition-metal chromophores with earth-abundant transition metals are an important design target for their applications in lighting and nontoxic bioimaging, but their design is challenged by the scarcity of complexes that simultaneously have well-defined ground states and optimal target absorption energies in the visible region. Machine learning (ML) accelerated discovery could overcome such ...

  7. Synthesis and Applications of Transition Metal Complexes

    Transition metal complexes have some of the most challenging, diverse, and interesting chemistry known. Consequently, they possess a wide array of applications, from medicinal to functional materials, but it is in homogeneous catalysis that transition metal complexes thrive. ... Research articles, review articles as well as short communications ...

  8. Luminescent and Photofunctional Transition Metal Complexes: From

    There has been emerging interest in the exploitation of the photophysical and photochemical properties of transition metal complexes for diagnostic and therapeutic applications. In this Perspective, we highlight the major recent advances in the development of luminescent and photofunctional transition metal complexes, in particular, those of rhenium(I), ruthenium(II), osmium(II), iridium(III ...

  9. Special Issue: Recent Advances in Transition‐Metal Catalysis

    Transition-metal catalysis has emerged as the most effective and reliable approach towards achieving asymmetric chemical transformations. The ability of transition-metal complexes to impart asymmetry in organic molecules through chiral ligands and chiral counterions has provided an access point to the enantioselective synthesis of numerous ...

  10. Photochemistry of transition metal complexes (2019-2020)

    This Chapter aims to summarise the major advances achieved over 2019 and 2020 in the field of photochemistry and photocatalysis by transition metal compounds. In the last years, one of the central research themes has been the development of efficient photocatalytic complexes based on earth-abundant metals as a potential eco-friendly, resource ...

  11. Journal of Transition Metal Complexes

    The Journal of Transition Metal Complexes is a scholarly open access, peer-reviewed, and fully refereed journal. It presents original papers, reviews, and communications on all aspects of theoretical and experimental transition metal complex chemistry. Original manuscripts are expected to provide a clear contribution to advances in the ...

  12. Schiff bases and their metal Complexes: A review on the history

    The majority of Schiff bases are attractive ligands since they construct complexation efficiently, with most transition metals owing to the tunable of the stereo-electronic structures [9], [10].Meanwhile, Schiff bases may also function as multifunctional ligands suitable for the coordination of a range of metallic ions with varying geometries and oxidization states.

  13. A review on versatile applications of transition metal complexes

    The research showed that the complexes could inhibit K562 tumour cell's growth, generation, and induce apoptosis. The inhibition ratio was accelerated by increasing the dosage, and it had significant positive correlation with the medication dosage. ... Transition metal complexes containing Schiff bases have been of much interest over the last ...

  14. Mining the right transition metals in a vast chemical space

    Kulik and her group focus on transition metal complexes, molecules comprised of metals found in the middle of the periodic table that are surrounded by organic ligands. These complexes can be extremely reactive, which gives them a central role in catalyzing natural and industrial processes. ... In a related research thrust, which they showcased ...

  15. Synthesis, characterization, and biological studies of some biometal

    The chemistry of transition metal complexes has received considerable attention largely due to their catalytic and bioinorganic relevance. Such complexes are also important due to their potential biological activities such as antibacterial, antifungal, antimalarial, and antitumor [1,2,3,4].Medicinal inorganic chemistry is comparatively a new discipline which developed after the serendipitous ...

  16. Experimental and theoretical insight of Schiff base transition metal

    The Schiff base complexes described in the present research article were synthesized as outlined in Scheme ... In the present study, a series of novel Schiff base divalent transition metal complexes of cobalt, copper, nickel and zinc have been synthesized. The complexes were characterized by various spectroscopic techniques that indicate the ...

  17. Late transition metal complexes of ferrocene‐containing nitrogen

    Applied Organometallic Chemistry covers organometallic and metal-organic chemistry of main group & transition metals, lanthanides & actinides. Bis(2-picolyl)amine (bpa), iminodiacetamide (imda), and bis-1,2,3-triazole (bta) ferrocene ligands (L) with and without an aliphatic linker were prepared by multi-step synthesis.

  18. Synthesis of Six New Transition Metal Complexes: Structural

    Three one-pot reactions leading to six new transition metal complexes are presented. The one-pot reactions involved transformations of 2-(N'-dicyanomethylene-hydrazino)-benzoic acid (DHB) into three new ligands (Lig-I) 2−, (Lig-II) 2−, and (Lig-III) 2−.The complex [Ni 2 (Lig-I) 2] ⋅ 3H 2 O (1) was prepared in a one-pot synthesis in which ligand, (Lig-I) 2− was formed by the ...

  19. (PDF) Transition metal complexes and their application in drugs and

    A transition metal complex, also known as a coordination complex, is an entity made up of a central metal atom or ion connected to a fixed number of ions or molecules known as ligands that are ...

  20. Atomically engineering metal vacancies in monolayer transition metal

    The capping PVP agent is prerequisite to induce metal vacancies via the e-beam sculpting approach, as discussed later. Upon e-beam irradiation of ~10 7 e − nm −2 during STEM imaging, a few ...

  21. Overview of the Synthesis and Catalytic Reactivity of Transition Metal

    The Ozawa research group reported that (π-allyl)palladium complexes (171A-C) ... Despite their monodentate nature, they well stabilize transition metal complexes. DPCB and BPEP are particularly important ligands that serve as sources of C═P binding, which may be related to the high stability these systems impart to transition metals. ...

  22. Magnetism of multinuclear 3-d transition metal complexes of 2

    Chapter 1 discusses the diversity of structure types used to study magneto structural correlations in 3-d transition metal complexes. The discussion is focussed on heterometallic examples with a nuclearity of 10 or less, highlighting significant examples used in the quantitative study of fundamental magnetic properties.

  23. Organic Synthesis via Transition Metal-Catalysis

    In recent years, the development of transition-metal-catalyzed reactions has acquired an increasing importance. In fact, the use of transition metal complexes as catalysts may allow performing important organic transformations in one synthetic step by the assembly of simple units under sustainable conditions [].This Special Issue reports significant contributions in this field.

  24. 19.2: Coordination Chemistry of Transition Metals

    Transition metal complexes often exist as geometric isomers, ... Her research combines the fields of fundamental inorganic and physical chemistry with materials engineering. She is working on many different projects that rely on transition metals. For example, one type of compound she is developing captures carbon dioxide waste from power ...

  25. Synthesis and Characterization of Metal Complexes with Schiff Base

    In order for undergraduate laboratory experiments to reflect modern research practice, it is essential that they include a range of elements, and that synthetic tasks are accompanied by characterization and analysis. This intermediate general chemistry laboratory exercise runs over 2 weeks, and involves the preparation of a Schiff base ligand and its metal (Fe3+ or Cu2+) complex. Students are ...

  26. 2.1.1: Introduction to transition metal complexes (coordination

    These compounds are called transition metal complexes or coordination complexes. They are often brightly-colored compounds and they sometimes play very useful roles as catalysts or even as pharmaceuticals. Because of their relatively low electronegativity, transition metals are frequently found as positively-charged ions, or cations. These ...