Synthesis, crystal structures and magnetic properties of new chromium(III)–acetylide–TTF type complexes

Abstract

Novel Cr(III)–acetylide–tetrathiafulvalene (TTF) type complexes, [Cr(III)Cyclam(CC-MeBMT-TTF)2]n+ ([1]n+, Cyclam=1,4,8,11-tetraazacyclotetradecane, MeBMT-TTF=5-methyl-4′,5′-bis(methylthio)tetrathiafulvalene) and [Cr(III)Cyclam(CC-MeEDO-TTF)2]n+ ([2]2+, MeEDO-TTF=5-methyl-4′,5′-ethylenedioxytetrathiafulvalene) were synthesized. Electrochemical oxidation of the complexes afforded [1](ClO4)3(PhCl), [2](ClO4)2(PhCl)(H2O)2 and [2][CrPhen(NCS)4]2(PhCl)2 (Phen=1,10-phenanthroline), where the adjacent TTF-type ligands of neighboring complexes form a (TTF)2n+ dimer that results in a 1D chain arrangement of [1]3+ or [2]2+. For [1](ClO4)3(PhCl), the singlet nature of a divalent TTF dimer results in a weak exchange interaction between the S=3/2 spins of Cr3+. By contrast, the TTF dimers in [2](ClO4)2(PhCl)(H2O)2 and [2][CrPhen(NCS)4]2(PhCl)2 are monovalent and have a spin of 1/2. The strong exchange interaction between the spins of the TTF dimer and Cr3+ results in the chain of [2]2+ being ferrimagnetic. The weak inter chain interaction and single-ion anisotropy of the TTF dimers in [2](ClO4)2(PhCl)(H2O)2 lead to weak ferromagnetic ordering at 21K.