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Inorganics
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Metal Complexes Diversity: Synthesis, Conformations, and Bioactivity
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Metal Complexes Diversity: Synthesis, Conformations, and Bioactivity

A special issue of Inorganics (ISSN 2304-6740). This special issue belongs to the section "Coordination Chemistry".

Deadline for manuscript submissions: 31 March 2025 | Viewed by 8114

Special Issue Editors

Dr. Sunčica Roca

E-Mail Website
Guest Editor
NMR Centre, Ruđer Bošković Institute, Bijenička 54, HR-10000 Zagreb, Croatia
Interests: NMR spectroscopy; conformations in solution; metal coordination chemistry; NMR of small organic molecules; NMR of natural compounds
Special Issues, Collections and Topics in MDPI journals
Dr. Monika Kovačević

E-Mail Website
Guest Editor
Department of Chemistry and Biochemistry, Faculty of Food Technology and Biotechnology, University of Zagreb, Pierottijeva 6, HR-10000 Zagreb, Croatia
Interests: ferrocene; conformational analysis; intramolecular hydrogen bonds; peptidomimetics; structure–activity relationship
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Metal complexes occupy a pivotal position across diverse fields, including catalysis, material science, and medicine. The rich diversity in their architecture stems from the intricate combinations of metal ions, ligands, and their distinct coordination modes. This variety not only shapes the conformational properties of these complexes but also profoundly impacts their biological activities.

The synthesis of metal complexes is a meticulous process that requires the careful selection of metal ions and ligands, along with the precise control of reaction conditions, to yield desired structures. The conformational properties of metal complexes are influenced by multiple factors, including the coordination geometry of metal ions, ligand flexibility, and intermolecular interactions. On the other hand, the biological activities of these complexes are intricately linked to their interactions with biological systems, such as enzymes, receptors, and nucleic acids.

In conclusion, this Special Issue delves into the fascinating realm of metal complex diversity, encompassing their architecture, synthesis, conformational properties, and biological activities. This comprehensive exploration holds immense promise for the advancement of new catalysts, materials, and drugs, offering enhanced performance and specificity.

Dr. Sunčica Roca
Dr. Monika Kovačević
Guest Editors

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Keywords

  • metal complexes
  • synthesis and conformation
  • SAR studies
  • biological evaluation
  • conformational analysis
  • spectroscopic methods
  • DFT calculations
  • bioactivity

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Published Papers (7 papers)

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Research

18 pages, 3144 KiB  
Article
Theoretical Study of the Effects of Different Coordination Atoms (O/S/N) on Crystal Structure, Stability, and Protein/DNA Binding of Ni(II) Complexes with Pyridoxal-Semi, Thiosemi, and Isothiosemicarbazone Ligand Systems
by Violeta Jevtovic, Aleksandra Rakić, Odeh A. O. Alshammari, Munirah Sulaiman Alhar, Tahani Alenezi, Violeta Rakic and Dušan Dimić
Inorganics 2024, 12(9), 251; https://doi.org/10.3390/inorganics12090251 - 17 Sep 2024
Cited by 1 | Viewed by 679
Abstract
Nickel transition metal complexes have shown various biological activities that depend on the ligands and geometry. In this contribution, six Ni(II) nitrate complexes with pyridoxal-semi, thiosemi, and isothiosemicarbazone ligands were examined using theoretical chemistry methods. The structures of three previously reported complexes ([Ni(PLSC)(H [...] Read more.
Nickel transition metal complexes have shown various biological activities that depend on the ligands and geometry. In this contribution, six Ni(II) nitrate complexes with pyridoxal-semi, thiosemi, and isothiosemicarbazone ligands were examined using theoretical chemistry methods. The structures of three previously reported complexes ([Ni(PLSC)(H2O)3]∙2NO3−, [Ni(PLTSC)2] ∙2NO3−∙H2O, and [Ni(PLITSC)(H2O)3]∙2NO3−) were investigated based on Hirshfeld surface analysis, and the most important stabilization interactions in the crystal structures were outlined. These structures were optimized at the B3LYP/6-311++G(d,p)(H,C,N,O,(S))/LanL2DZ(Ni) level of theory, and the applicability was checked by comparing theoretical and experimental bond lengths and angles. The same level of theory was applied for the optimization of three additional structures, ([Ni(PLSC)2]2+, [Ni(PLTSC)(H2O)3]2+, and [Ni(PLITSC)2]2+). The interactions between selected ligands and Ni(II) were examined using the Natural Bond Orbital (NBO) and Quantum Theory of Atoms in Molecules (QTAIM) approaches. Particular emphasis was placed on interactions between oxygen, sulfur, and nitrogen donor atoms and Ni(II). Human Serum Albumin (HSA) and the DNA-binding properties of these complex cations were assessed using molecular docking simulations. The presence of water molecules and various substituents in the thermodynamics of the processes was demonstrated. The results showed significant effects of structural parameters on the stability and reactivity towards important biomolecules. Full article
(This article belongs to the Special Issue Metal Complexes Diversity: Synthesis, Conformations, and Bioactivity)
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16 pages, 2220 KiB  
Article
A New Azide-Bridged Polymeric Manganese (III) Schiff Base Complex with an Allylamine-Derived Ligand: Structural Characterization and Activity Spectra
by Aynaz Talebi, Mehdi Salehi, A. J. Lopes Jesus, Maciej Kubicki, Rui Fausto and Reza Golbedaghi
Inorganics 2024, 12(9), 234; https://doi.org/10.3390/inorganics12090234 - 28 Aug 2024
Viewed by 726
Abstract
This paper reports the synthesis and structural characterization of a novel azide-bridged polymeric manganese (III) Schiff base complex, using 2-((allylimino)methyl)-6-ethoxyphenol as a ligand. The crystal structure of the synthesized compound, elucidated by single-crystal X-ray diffraction analysis, indicates that it crystallizes in the monoclinic [...] Read more.
This paper reports the synthesis and structural characterization of a novel azide-bridged polymeric manganese (III) Schiff base complex, using 2-((allylimino)methyl)-6-ethoxyphenol as a ligand. The crystal structure of the synthesized compound, elucidated by single-crystal X-ray diffraction analysis, indicates that it crystallizes in the monoclinic space group P21/c. The complex is found to display an octahedral geometry in which the central manganese Mn(III) coordinates with two bidentate donor Schiff base ligands via oxygen and nitrogen atoms. In addition, the metallic centers are linked together to form a one-dimensional chain bridged by end-to-end azide ligands. To offer a more thorough characterization of the synthesized compound, the study incorporates experimental data from FT-IR, UV-Vis, and cyclic voltammetry, alongside computational results from Hirshfeld surface analysis and DFT calculations conducted for both the ligand and complex. The computational analyses provided valuable insights into the intrachain and interchain interactions within the crystal structure, clarified the conformational characteristics of the isolated ligand molecule, and aided in the interpretation of the experimental IR spectra. Furthermore, an assessment of the compound’s drug-like properties was conducted using activity spectra for substances (PASS) predictions, revealing potential pharmacological activities. Full article
(This article belongs to the Special Issue Metal Complexes Diversity: Synthesis, Conformations, and Bioactivity)
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17 pages, 3948 KiB  
Article
Thionitrosyl Complexes of Rhenium and Technetium with PPh3 and Chelating Ligands—Synthesis and Reactivity
by Domenik Nowak, Adelheid Hagenbach, Till Erik Sawallisch and Ulrich Abram
Inorganics 2024, 12(8), 210; https://doi.org/10.3390/inorganics12080210 - 31 Jul 2024
Cited by 1 | Viewed by 1014
Abstract
In contrast to corresponding nitrosyl compounds, thionitrosyl complexes of rhenium and technetium are rare. Synthetic access to the thionitrosyl core is possible by two main approaches: (i) the treatment of corresponding nitrido complexes with S2Cl2 and (ii) by reaction of [...] Read more.
In contrast to corresponding nitrosyl compounds, thionitrosyl complexes of rhenium and technetium are rare. Synthetic access to the thionitrosyl core is possible by two main approaches: (i) the treatment of corresponding nitrido complexes with S2Cl2 and (ii) by reaction of halide complexes with trithiazyl chloride. The first synthetic route was applied for the synthesis of novel rhenium and technetium thionitrosyls with the metals in their oxidation states “+1” and “+2”. [MVNCl2(PPh3)2], [MVNCl(PPh3)(LOMe)] and [MVINCl2(LOMe)] (M = Re, Tc; {LOMe}− = (η5-cyclopentadienyl)tris(dimethyl phosphito-P)cobaltate(III)) complexes have been used as starting materials for the synthesis of [ReII(NS)Cl3(PPh3)2] (1), [ReII(NS)Cl3(PPh3)(OPPh3)] (2), [ReII(NS)Cl(PPh3)(LOMe)]+ (4a), [ReII(NS)Cl2(LOMe)] (5a), [TcII(NS)Cl(PPh3)(LOMe)]+ (4b) and [TcII(NS)Cl2(LOMe)] (5b). The triphenylphosphine complex 1 is partially suitable as a precursor for ongoing ligand exchange reactions and has been used for the synthesis of [ReI(NS)(PPh3)(Et2btu)2] (3a) (HEt2btu = N,N-diethyl-N′-benzoyl thiourea) containing two chelating benzoyl thioureato ligands. The novel compounds have been isolated in crystalline form and studied by X-ray diffraction and spectroscopic methods including IR, NMR and EPR spectroscopy and (where possible) mass spectrometry. A comparison of structurally related rhenium and technetium complexes allows for conclusions about similarities and differences in stability, reaction kinetics and redox behavior between these 4d and 5d transition metals. Full article
(This article belongs to the Special Issue Metal Complexes Diversity: Synthesis, Conformations, and Bioactivity)
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18 pages, 1867 KiB  
Article
Conformational, Electrochemical, and Antioxidative Properties of Conjugates of Different Ferrocene Turn-Inducing Scaffolds with Hydrophobic Amino Acids
by Monika Kovačević, Sunčica Roca, Dijana Jadreško, Jasna Mrvčić, Karla Hanousek Čiča, Mojca Čakić Semenčić and Lidija Barišić
Inorganics 2024, 12(7), 195; https://doi.org/10.3390/inorganics12070195 - 18 Jul 2024
Viewed by 674
Abstract
The incorporation of different ferrocene scaffolds into the peptide sequences induces the formation of hydrogen-bond-based secondary structural elements that are frequently observed in natural peptides and proteins. There are three simple ferrocene scaffolds for conjugation with amino acids and peptides that serve as [...] Read more.
The incorporation of different ferrocene scaffolds into the peptide sequences induces the formation of hydrogen-bond-based secondary structural elements that are frequently observed in natural peptides and proteins. There are three simple ferrocene scaffolds for conjugation with amino acids and peptides that serve as templates for ferrocene peptidomimetics, namely ferrocene-1,1′-dicarboxylic acid (Fcd, I), 1′-aminoferrocene-1-carboxylic acid (Fca, III), and ferrocene-1,1′-diamine (Fcda, V). Here, we have investigated their ability to induce the turn structure upon conjugation with Val, Leu, and Phe. Furthermore, we also wanted to determine whether the branched side chains of Val, Leu, and Phe interfere with intramolecular hydrogen bonding (IHB). For these purposes, we performed a detailed spectroscopic analysis by measuring the concentration, temperature, and solvent dependence of the IR, NMR, and CD spectra. The effect of the different ferrocene scaffolds on the antioxidant activity of the prepared peptides was tested using the DPPH and ABTS methods, and was further rationalized using electrochemical measurements. It was found that the ferrocene scaffold has the greatest influence on the hydrogen bonding pattern, while the influence of the side branches of the amino acids is less relevant. Full article
(This article belongs to the Special Issue Metal Complexes Diversity: Synthesis, Conformations, and Bioactivity)
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12 pages, 4896 KiB  
Article
Electronic and Steric Effects on Oxygen Reactivities of NiFeSe Complexes Related to O2-Damaged [NiFeSe]-Hydrogenases’ Active Site
by Yuchen Qiao, Enting Xu, Yameng Hao, Xuemei Yang and Ming Ni
Inorganics 2024, 12(6), 163; https://doi.org/10.3390/inorganics12060163 - 10 Jun 2024
Viewed by 1014
Abstract
Hydrogen has the potential to serve as a new energy resource, reducing greenhouse gas emissions that contribute to climate change. Natural hydrogenases exhibit impressive catalytic abilities for hydrogen production, but they often lack oxygen tolerance. Oxygen-tolerant hydrogenases can work under oxygen by reacting [...] Read more.
Hydrogen has the potential to serve as a new energy resource, reducing greenhouse gas emissions that contribute to climate change. Natural hydrogenases exhibit impressive catalytic abilities for hydrogen production, but they often lack oxygen tolerance. Oxygen-tolerant hydrogenases can work under oxygen by reacting with oxygen to form inactive states, which can be reactivated to catalytic states by oxygen atom removal. Herein, we synthesized three NiFeSe complexes: (NiSe(CH3)FeCp, NiSe(CH3)FeCp* and NiSe(PhNMe2)FeCp) with features of active sites of [NiFeSe]-H2ases, which are the oxygen-tolerant hydrogenases, and we investigated the influence of electronic and steric factors on the oxygen reaction of these “biomimetic” complexes. In our research, we found that they react with oxygen, forming 1-oxygen species, which is related to the O2-damaged [NiFeSe] active site. Through a comparative analysis of oxygen reactions, we have discovered that electronic factors and steric hindrance on Se play a significant role in determining the oxygen reactivity of NiFe complexes related to hydrogenases’ active sites. Full article
(This article belongs to the Special Issue Metal Complexes Diversity: Synthesis, Conformations, and Bioactivity)
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13 pages, 1952 KiB  
Article
Synthesis, Properties, and Electrochemistry of bis(iminophosphorane)pyridine Iron(II) Pincer Complexes
by Nicolás Sánchez López, Erick Nuñez Bahena, Alexander D. Ryabov, Pierre Sutra, Alain Igau and Ronan Le Lagadec
Inorganics 2024, 12(4), 115; https://doi.org/10.3390/inorganics12040115 - 16 Apr 2024
Viewed by 1780
Abstract
Iron derivatives have emerged as valuable catalysts for a variety of transformations, as well as for biological and photophysical applications, and iminophosphorane can be considered an ideal ligand scaffold for modulating electronic and steric parameters in transition metal complexes. In this report, we [...] Read more.
Iron derivatives have emerged as valuable catalysts for a variety of transformations, as well as for biological and photophysical applications, and iminophosphorane can be considered an ideal ligand scaffold for modulating electronic and steric parameters in transition metal complexes. In this report, we aimed to synthesize dichloride and dibromide iron(II) complexes supported by symmetric bis(iminophosphorane)pyridine ligands, starting from readily available ferrous halides. The ease of synthesis of this class of ligands served to access several derivatives with distinct electronic and steric properties imparted by the phosphine moiety. The ligands and the resulting iron(II) complexes were characterized by 31P and 1H NMR spectroscopy and DART or ESI mass spectrometry. While none of these iron(II) complexes could be characterized by single-crystal X-ray diffraction, suitable crystals of a µ-O bridged dinuclear iron complex bearing an iminophosphorane ligand were obtained, confirming a κ3 binding motif. The bis(iminophosphorane)pyridine ligands in the obtained iron(II) complexes are labile, as demonstrated by their facile substitution by terpyridine. Cyclic voltammetry studies revealed that the oxidation of bis(iminophosphorane)pyridine iron(II) complexes to iron(III) species is quasi-reversible, suggesting the strong thermodynamic stabilization of the iron(III) center imparted by the σ-donating iminophosphorane ligands. Full article
(This article belongs to the Special Issue Metal Complexes Diversity: Synthesis, Conformations, and Bioactivity)
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15 pages, 3237 KiB  
Article
Synthesis, Spectral Characterization, and Structural Modelling of Di- and Trinuclear Iron(III) Monensinates with Different Bridging Patterns
by Nikolay Petkov, Alia Tadjer, Svetlana Simova, Zara Cherkezova-Zheleva, Daniela Paneva, Radostina Stoyanova, Rositsa Kukeva, Petar Dorkov and Ivayla Pantcheva
Inorganics 2024, 12(4), 114; https://doi.org/10.3390/inorganics12040114 - 15 Apr 2024
Cited by 1 | Viewed by 1637
Abstract
In the present study, we report the solid-state isolation and structural characterization of novel iron(III) complexes of the veterinary antibiotic monensin. Monensic acid (MonH × H2O) forms a dinuclear complex of composition with FeCl3 [FeCl(Mon)2]2 (1 [...] Read more.
In the present study, we report the solid-state isolation and structural characterization of novel iron(III) complexes of the veterinary antibiotic monensin. Monensic acid (MonH × H2O) forms a dinuclear complex of composition with FeCl3 [FeCl(Mon)2]2 (1), while its interaction with FeSO4 leads to the isolation of a triangular oxo-ferric coordination species [Fe3O(Mon × H2O)6(H2O)2(OH)] (2). During the procedure resulting in 2, oxidation of the Fe(II) ions by atmospheric oxygen was observed. In the presence of organic bases, both complexation reactions proceeded to successfully deprotonate the carboxylic function of the ligand. Iron(III) complexes 1 and 2 were characterized by IR, EPR, NMR, and Mössbauer spectroscopies as well as with thermal (TG-DTA/MS) and elemental analyses. In addition, the structures of the two coordination compounds were modelled and selected calculated parameters were compared with the experimental results. The biological assay revealed the enhanced antibacterial potential of the newly obtained complexes against the Gram-positive aerobic microorganisms Bacillus cereus and Bacillus subtilis. Full article
(This article belongs to the Special Issue Metal Complexes Diversity: Synthesis, Conformations, and Bioactivity)
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