Synthesis, Characterization, and Reactivity of Mononuclear O,N-Chelated Vanadium(IV) and -(III) Complexes of Methyl 2-Aminocyclopent-1-ene-1-dithiocarboxylate Based Ligand: Reporting an Example of Conformational Isomerism in the Solid State

Vanadium(IV) and -(III) complexes of a tetradentate N2OS Schiff base ligand H2L [derived from methyl 2-((β-aminoethyl)amino)cyclopent-1-ene-1-dithiocarboxylate and salicylaldehyde] are reported. In all the complexes, the ligand acts in a bidentate (N,O) fashion leaving a part containing the N,S donor set uncoordinated. The oxovanadium(IV) complex [VO(HL)2] (1) is obtained by the reaction between [VO(acac)2] and H2L. In the solid state, compound 1 has two conformational isomers 1a and 1b; both have been characterized by X-ray crystallography. Compound 1a has the syn conformation that enforces the donor atoms around the metal center to adopt a distorted tbp structure (τ = 0.55). Isomer 1b on the other hand has an anti conformation with almost a regular square pyramidal geometry (τ = 0.06) around vanadium. In solution, however, 1 prefers to be in the square pyramidal form. A second variety of vanadyl complex [VO(Lcyclic)2](I3)2 (2) with a new bidentate O,N donor ligand involving isothiazolium moiety has been obtained by a ligand-based oxidation of the precursor complex 1 with iodine. Preliminary X-ray and FAB mass spectroscopic data of 2 have supported the formation of a heterocyclic moiety by a ring closure reaction involving a N−S bond. Vanadium(III) complex [V(acac)(HL)2] (3) has been obtained through partial ligand displacement of [V(acac)3] with H2L. Compound 3 has almost a regular octahedral structure completed by two bidentate HL ligands along with an acetylacetonate molecule. Electronic spectra, magnetism, EPR, and redox properties of these compounds are reported.