Oxovanadium(V) and Cobalt(III) Complexes of Dithiocarbazate-Based Schiff Base Ligands: Formation of a Thiadiazole Ring by Vanadium-Induced Cyclization of the Coordinated Ligand

S-Methyl 3-((2-hydroxyphenyl)methyl)dithiocarbazate (H2L1) and its bromo derivative (H2L2), which are traditionally
biprotic tridentate (ONS) ligands, behave in an unprecedented manner when allowed to react with [VO(acac)2]
under an oxidative environment in acetonitrile−water medium containing a catalytic amount of alkali metal ion. The
products obtained are oxovanadium(V) compounds [VOL(Lcyclic)] (L = L1, 1a, and L2, 1b) that contain one molecule
of ligand which undergoes metal-induced cyclization to form a thiadiazole ring. Compound 1a crystallizes in the
triclinic space group P1̄ with a = 9.1830(9) Å, b = 9.4165(12) Å, c = 12.700(2) Å, α = 100.988(8)o, β =
100.195(7)o, γ = 78.774(8)o, V = 1046.3(2) Å3, and Z = 2. With cobalt(III), however, the products [CoL(HL)]·H2O
(L = L1, 2a, and L2, 2b) have hydrogen-bonded dimeric structures with each ligand virtually carrying 1.5 units of
negative charge as confirmed by X-ray crystal structure analysis of 2a. It also crystallizes in triclinic space group
P1̄ with a = 12.0842(8) Å, b = 13.5251(9) Å, c = 14.1960(10) Å, α = 78.122(6)o, β = 73.888(6)o, γ = 78.255(6)o, V = 2154.7(3) Å3, and Z = 4. In solution, 2a is a symmetric molecule as indicated by 1H NMR, involving a
characteristic hydrogen-bonded O−H−O broad feature in the downfield (at 14.5 ppm) connecting both monoprotonated
(LH-) and deprotonated (L2-) forms of the liganda situation somewhat analogous to the classic H−F−H case as
observed in bifluoride ion.