New alkoxooxovanadium(V) complexes, [VO(L)(OR)] (OR = OMe (1), OEt (2), OPr (3)), were synthesized by the reaction of assorted vanadium precursors and 4-methoxysalicylaldehyde 4-phenylthiosemicarbazone (H2L) in appropriate alcohols. Complexes 2 and 3 crystallized each in two polymorphic forms, which can be selectively prepared by using either a vanadium(IV) or a vanadium(V) precursor. The conformational flexibility of these complexes manifests itself in conformational polymorphism (2a and 2b, 3a, and 3b), conformational isomorphism (2b, 3a, and 3b), and conformational synmorphism (3a and 3b). The largest conformational differences are found in the spatial arrangements of the coordinated alkoxo groups and the phenyl rings of the ligand. The isostructurality of complexes 2b and 3a reflects, on the other hand, their conformational similarity, with nearly the same pattern of intermolecular interactions dominating within their crystal architectures. However, unlike the case in 3a, the structure of 2b exhibits ...

Conformational Diversity of Thiosemicarbazonatovanadium(V) Complexes in the Solid State: From Polymorphism to Isostructurality

The reaction of 2,5-bis[N,N′-bis(2-pyridyl-aminomethyl)aminomethyl]-p-hydroquinone (H2bpymah) with VO2+ salts in acetonitrile or water at a low pH (2.2–3.5) results in the isolation of [{VIV(O)(Cl)}2(μ-bpymah)], the p-semiquinonate complex [{VIV(O)(Cl)}2(μ-bpymas)](OH), the cyclic mixed-valent hexanuclear compound [{VV(O)(μ-O)VIV(O)}(μ-bpymah)]3, and [(VVO2)2(μ-bpymah)]. [{VIV(O)(Cl)}2(μ-bpymas)](OH) is an intermediate of the radical-mediated oxidation of [{VIV(O)(Cl)}2(μ-bpymah)] from O2. At lower pH values (2.2), a reversible intramolecular electron transfer from the metal to the ligand of [{VIV(O)(Cl)}2(μ-bpymas)](OH) is induced with the concurrent substitution of chlorine atoms by the oxygen-bridging atoms, resulting in the formation of [{VV(O)(μ-O)VIV(O)}(μ-bpymah)]3. The metal complexes were fully characterized by X-ray crystallography, infrared (IR) spectroscopy, and magnetic measurements in the solid state, as well as by conductivity measurements, UV–vis spectroscopy, and electrochemical measureme...

Aerial Oxidation of a VIV–Iminopyridine Hydroquinonate Complex: A Trap for the VIV–Semiquinonate Radical Intermediate

[Zn(H2O)6][{Zn(H2O)}2(ttha)]·4H2O (ttha = triethylenetetraamine-N,N,N′,N″,N‴,N‴-hexaacetate) has been structurally characterized (triclinic, P-1, a = 7.4014(4) A, b = 8.5521(4) A, c = 15.0309(7) A, α = 73.582(1)°, β = 85.173(1)°, γ = 69.935(1)°; V = 857.15(7) A3; Z = 1). The two Zn2+ ions bound by the [ttha]−6 ligand are in distorted octahedral environments. While there exists a center of symmetry in the [{Zn(H2O)}2(ttha)]2− anion in the crystalline state, 13C{1H} NMR spectroscopy demonstrates the absence of a center of symmetry in aqueous solution. Furthermore, electronic absorption spectroscopy reveals that [Zn(H2O)6][{Zn(H2O)}2(ttha)]·4H2O reacts with vanadyl(IV) acetate in aqueous solution at room temperature to yield [(VO)2(ttha)]2−. This reaction implies that Zn2+ can dissociate from [{Zn(H2O)}2(ttha)]2− in aqueous solution. [Zn(H2O)6][{Zn(H2O)}2(ttha)]·4H2O (ttha = triethylenetetraamine-N,N,N′,N″,N‴,N‴-hexaacetate) has been structurally characterized by single crystal X-ray diffraction and has been found to undergo a transmetallation reaction with vanadyl(IV) acetate, yielding [(VO)2(ttha)]2−.

The X-Ray Structure and Spectroscopic Characterization of [Zn(H2O)6][{Zn(H2O)}2(ttha)]·4H2O (ttha = Triethylenetetraamine-N,N,N′,N″,N‴,N‴-hexaacetate)

Spectroscopic and structural characterization of Na2[(VO)2(ttha)]·8H2O (ttha = triethylenetetraamine-N,N,N',N ,N''',N'''-hexaacetate): Interpreting the results with density functional theory

In order to create new oral vanadyl organic complexes-based drugs for the treatment of diabetes mellitus biligand vanadyl derivative of L-malic acid (bis(L-malato)oxovanadium(IV) was prepared and its potential as a novel hypoglycemic agent was studied in the streptozotocin-diabetic rats. We show that the oral administration of bis(L-malato)oxovanadium(IV) with drink water significantly reduced glucose concentration in blood and urine, as well as the level of glycated proteins in the streptozotocin-diabetic rats.

C. W. Weston

Papers

Vanadyl(IV) Acetate, VO(CH3CO2)2