Liquid-crystalline oxovanadium(IV) complexes accessed from bidentate [N, O] donor salicylaldimine Schiff-base ligands

A series of bis[4-(n-alkoxy)-N-(4'-R-phenyl)salicylideneiminato]oxovanadium(IV) complexes (n = 6, 10, 14, 16, 18 and R = C3H7) were prepared and their mesogenic properties were investigated. The mesomorphic behaviors of the compounds were studied by polarized optical microscopy and differential scanning calorimetry. Ligands display SmA/SmC and unexpected nematic mesophases. The complexes bearing longer alkoxy carbon chain (n = 10, 14, 16, and 18) showed both monotropic or enantiotropic transitions with smectic A and high ordered smectic E phases. However, the complex with shorter carbon chain length (n = 6) showed monotropic transition with an unprecedented nematic (N) phase. A density functional theory study was carried out using DMol3 at BLYP/DNP level to obtain a stable optimized structure. A square-pyramidal geometry for the vanadyl complexes has been suggested. A nu(V=O) stretching value of similar to 970 cm(-1) corroborated absence of any V=O center dot center dot center dot V=O interactions. Cyclic voltammetry revealed a quasireversible one-electron response at 0.61 V for the VO(IV)-VO(V) redox couple. Variable temperature magnetic susceptibility measurements of the vanadyl complexes suggested absence of any exchange interactions among the vanadyl spin centers.