Synthesis, Structures and Ion‐Association Properties of a Series of Schiff Base Oxidovanadium(V) Complexes with 4‐Substituted Long Alkoxy Chains

Abstract

AbstractSchiff base VO2V and VOV complexes with long 4‐substituted alkoxy chains have been synthesised from the corresponding VOIV complexes, [VO{(4‐CnH2n+1O)xsalen}] [x = 1, 2, n = 3–16 and salen = N,N′‐ethylenebis(salicylideneiminato)], in solutions in the absence or presence of HClO4 under aerobic conditions. The green single‐crystals of the VOIV complexes (x = 2, n = 3, 4, 6) coexisting with solutions without HClO4 turned slowly to the yellow single‐crystals of the species with n = 3 (1) and 4 (2), a process which took several months. An X‐ray crystallographic analysis revealed that the VOIV complexes are transformed into the dimeric VO2V complexes with the tridentate sal‐en (sal‐en = N‐salicylideneethylenediamine) ligand from the tetradentate salen moieties. However, the single crystals of the VOIV complexes with longer alkoxy chains of n ≥ 8 did not yield the corresponding yellow crystals of the VO2V complexes. This crystal‐to‐crystal transformation is discussed in relation to the crystal packing structures of the VOIV complexes. In contrast, addition of HClO4 solution to two series with one and two alkoxy chains in the 4‐positions immediately afforded the corresponding blue VOV perchlorate complexes, [VO{(4‐CnH2n+1O)xsalen}]ClO4 (x = 1, 2) without transformation of the salen moieties. The structure of 8·MeOH·0.5H2O determined from an X‐ray crystallographic analysis was a unique dimeric structure supported by electrostatic stacking and CH–π interactions in an octahedral environment. The DFT calculations were studied to obtain the stabilisation energy for the dimerisation. Furthermore, in methanol solution, the effects of the alkoxy chain lengths on the ion association were investigated by conductivity measurements. The ion‐association state in methanol solution is discussed with the solid‐state structure.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)