Structural aspects of molybdenum(IV), molybdenum(V) and molybdenum(VI) complexes

A new series of bioactive Mo(V)2O2S2-based thiosemicarbazone complexes: Solution and DFT studies, and antifungal and antioxidant activities

This paper deals with the synthesis, characterization, and studies of biological properties of a series of 5 coordination compounds based on binuclear core [Mo(V)2O2S2]2+ with thiosemicarbazones ligands bearing different substituents on the R1 position of the ligand. The complexes are first studied using MALDI-TOF mass spectrometry and NMR spectroscopy to determine their structures in solution in relation to single-crystal X-Ray diffraction data. In a second part, the antifungal and antioxidative activities are explored and the high potential of these coordination compounds compared to the uncoordinated ligands is demonstrated for these properties. Finally, DFT calculation provides important support to the solution studies by identifying the most stable isomers in each [Mo2O2S2]2+/Ligand system, while the determination of HUMO and LUMO levels is performed to explain the antioxidative properties of these systems.

Tuning the nuclearity of [Mo2O2S2]2+-based assemblies by playing with the degree of flexibility of bis-thiosemicarbazone ligands

[MoV2O₂S₂]²⁺-based thiosemicarbazone complexes appear as very promising molecules for biological applications due to the intrinsic properties of their components. This paper deals with the synthesis and characterization of six coordination complexes obtained by the reaction of [MoV2O₂S₂]²⁺ clusters with bis-thiosemicarbazone ligands that contain flexible or rigid spacers between the two thiosemicarbazone units. Interestingly, structural characterization by single-crystal X-ray diffraction, MALDI-TOF MS technique and NMR spectroscopy revealed that the nuclearity of the complex is controlled by the nature of the spacer between the thiosemicarbazone units. Binuclear complexes, namely [MoV2O₂S₂(L^1-3)], are isolated with flexible spacers while tetranuclear complexes [(MoV2O₂S₂)₂(L^4-6)₂] are formed when the bis-thiosemicarbazone ligands are built on rigid spacers.

Synthesis, Structures, and Solution Studies of a New Class of [Mo2O2S2]-Based Thiosemicarbazone Coordination Complexes

This paper deals with the synthesis, structural studies, and behavior in solution of unprecedented coordination complexes built by the association of a panel of 14 representative thiosemicarbazone ligands with the cluster [Mo₂O₂S₂]²⁺. These complexes have been thoroughly characterized both in the solid state and in solution by XRD and by NMR, respectively. In particular, HMBC ¹H{¹⁵N} and ¹H DOSY NMR experiments bring important elements for understanding the complexes' behavior in solution. These studies demonstrate that playing on the nature and the position of various substituents on the ligands strongly influences the coordination modes of the ligands as well as the numbers of isomers in solution, mainly 2 products for the majority of complexes and up to 5 for some of them.

Viking Helmet Corroles: Activating Inert Oxidometal Corroles

Chemically inert oxidometal(V) corrols of molybdenum and rhenium undergo clean ligand-exchange reactions upon the action of SiCl₄ . The resulting dichlorido complexes show trigonal prismatic coordination of the metal ion with the chlorine atoms residing in a cis configuration, and were studied by optical and resonance spectroscopy as well as DFT calculations. In situ reactivity studies with carbon nucleophiles indicate high reactivity for chlorine replacement. Treatment with sodium cyclopentadienide paves the way to robust molybdenum corrolocene half-sandwich complexes. These organometallic compounds are the first corrole species that stabilize an air-stable and diamagnetic low spin d² -Mo^IV center. Structural, spectroelectrochemical, and chemical investigations prove a reversible Mo^IV /Mo^V redox couple close to the Fc/Fc⁺ potential for these systems. The high stability of the compounds in both redox states calls for future applications in catalysis and as redox switch.

Synthesis and Catalytic Epoxidation Activity with TBHP and H2O2 of Dioxo-, Oxoperoxo-, and Oxodiperoxo Molybdenum(VI) and Tungsten(VI) Compounds Containing Monodentate or Bidentate Phosphine Oxide Ligands: Crystal Structures of WCl2(O)2(OPMePh2)2, WCl2(O)(O2)(OPMePh2)2, MoCl2(O)2dppmO2·C4H10O, WCl2(O)2dppmO2, Mo(O)(O2)2dppmO2, and W(O)(O2)2dppmO2

The dioxo tungsten(VI) and molybdenum(VI) complexes WCl2(O)2(OPMePh2)2, WCl2(O)2dppmO2, and MoCl2(O)2dppmO2, the oxoperoxo compounds WCl2(O)(O2)(OPMePh2)2, WCl2(O)(O2)dppmO2, and MoCl2(O)(O2)dppmO2, and the oxodiperoxo complexes, W(O)(O2)2dppmO2 and Mo(O)(O2)2dppmO2 have been prepared and characterized by IR spectroscopy, 31P NMR spectroscopy, elemental analysis, and X-ray crystallography. The structural and X-ray crystallographic data of compounds WCl2(O)2(OPMePh2)2, WCl2(O)(O2)(OPMePh2)2, MoCl2(O)2dppmO2.4H10O, WCl2(O)2dppmO2, Mo(O)(O2)2dppmO2, and W(O)(O2)2dppmO2 are also detailed. All complexes were studied as catalysts for cis-cyclooctene epoxidation in the presence of tert-butyl hydroperoxide (TBHP) or H2O2 as an oxidant. The Mo-based catalysts showed a superior reactivity over W-based catalysts in the TBHP system. On the other hand, in the H2O2 system, the W-based catalysts (accomplishing nearly 100% epoxidation of cyclooctene in 6 h) are more reactive than the Mo catalysts (<45% under some conditions). Various solvent systems have been investigated, and ethanol is the most suitable solvent for the H2O2 system.

Molybdenum(VI) Peroxo alpha-Amino Acid Complexes: Synthesis, Spectra, and Properties of MoO(O(2))(2)(alpha-aa)(H(2)O) for alpha-aa = Glycine, Alanine, Proline, Valine, Leucine, Serine, Asparagine, Glutamine, and Glutamic Acid. X-ray Crystal Structures of the Glycine, Alanine, and Proline Compounds

The compounds MoO(O(2))(2)(alpha-aa)(H(2)O), alpha-aa = glycine (1), alanine (2), proline (3), valine (4), leucine (5), serine (6), asparagine (7), glutamine (8), and glutamic acid (9), were prepared from the acidic aqueous solutions and characterized by examination of their IR, (1)H and (13)C NMR, and UV-visible spectra. They represent the first complexes containing a peroxo-alpha-amino acid combination in a metal ion ligand sphere. The synthesis and crystallization of these complexes was pH and concentration dependent, and their stability varied for different alpha-amino acids. X-ray structural studies of 1-3 have shown that the alpha-amino acids are coordinated as a zwitterion via one oxygen. This oxygen of the monodentate carboxylato group occupies an equatorial position in a distorted pentagonal bipyramid and encloses the pentagonal ring with the two bidentate peroxo groups. The apical positions are occupied by an oxo group and a water molecule, respectively. The Mo-O(O(2)) bonds are nonsymmetrical, differing in length by 0.009-0.045 Å. The longer bonds are located next to the coordinated carboxylato oxygen. A correlation between O-O and Mo-O bond lengths with the IR and UV-visible spectra of complexes 1-3 is discussed. Crystal structure of MoO(O(2))(2)(alanine)(H(2)O): monoclinic, space group P2(1)/c; Z = 4; a = 10.727(3) Å; b = 8.026(2) Å; c = 10.794(4) Å; beta = 110.81(2) degrees; V = 869 (Å)(3); R = 0.041. (1)H and (13)C NMR spectra in D(2)O solutions showed the presence of one complex species, which decomposed by standing in solution. Analogies and differences between Mo(VI) and V(V) peroxo complexes are outlined.