Mono- and polynuclear vanadium(IV) and -(V) compounds with 2-substituted phenyl/pyridyl heterocyclic chelates

In this account, we report the isolation of novel vanadium(IV) and -(V) compounds with 2-substituted phenyl/pyridyl heterocyclic chelates. The 1:2 molar reaction between NH4VO3 and 2-hydroxyphenylbenzothiazole (Hobs) led to the formation of a polynuclear vanadium(IV) compound, [VO(obs)(2)](n) (1). A trigonal bipyramidal mononuclear complex, cis-[VO2(obz)py] (2) was formed from the reaction of NH4VO3 and 2-hydroxyphenylbenzimidazole (Hobz) in the presence of pyridine. The novel octahedral vanadium(IV) complex, [VO(Hpbyz)(2)SO4] (3).H2O was afforded from the 2:1 molar reaction between 2-pyridylbenzimidazole (Hpybz) and VOSO4. These metal compounds were characterized by means of conductance measurements, UV-Vis, Emission, EPR, IR, V-51- and H-1 NMR spectroscopy as well as single crystal X-ray diffraction. The difference between the electronic properties of the respective metallic compounds are emphasized by the intense intra-ligand (pi-pi*) relaxations observed in the emission spectra of 1 (at 466 nm) and 2 (469 nm) while no emission spectrum could be attained for 3. The X-ray studies revealed that in 1 and 2, the chelating moieties act as monoanionic bidentate chelators (i.e. obs or obz) through the deprotonated phenolic oxygens and neutral heterocyclic nitrogens whereas a N-py,N-bz-coordination mode of the neutral Hpbyz chelators are observed in 3. (C) 2014 Elsevier Ltd. All rights reserved.