Synthesis, X-ray crystal structures and properties of chromium complexes with semiquinonate and catecholate

Abstract

The reaction of tris-tetrahalogeno-o-benzosemiquinonate chromium(III) complexes, [CrIII(X4SQ)3] (X = Cl 1a or Br 1b), with bis(cyclopentadienyl) cobalt [CoIICp2], tetramethyltetraselenafulvalene (TMTSF) and tetrakis(methylsulfanyl)tetrathiafulvalene (TMT-TTF) afforded four charge-transfer compounds, [CoIIICp2][CrIII(X4SQ)2(X4Cat)] (X = Cl 2a or Br 2b), [TMT-TTF][CrIII(Br4SQ)2(Br4Cat)] 3b and [TMTSF][CrIII(Br4SQ)2(Br4Cat)] 4b, where Cat is catecholate. The paramagnetic [CrIII(X4SQ)2(X4Cat)]– complexes are commonly formed by cocrystallization with a diamagnetic [CoIIICp2]+ cation for 2a·C6H6 and 2b, and paramagnetic TMT-TTF˙+ and TMTSF˙+ cations for 3b·C6H5CH3 and 4b·2CH2Cl2, respectively. The one-electron reduced complexes, [CrIII(X4SQ)2(X4Cat)]–, with two semiquinonate and one catecholate ligands were isolated and crystallographically characterized. The crystal structures of 2a·C6H6 and 3b·C6H5CH3 consist of alternating stacks of cations and anionic complexes, which form one-dimensional column structures. On the other hand, the anionic complexes in 4b·2CH2Cl2 form a hexagonal honeycomb network, whose cavities are occupied by the dimerized cation molecules. The temperature dependence of the magnetic susceptibilities reveals that all the [CrIII(X4SQ)2(X4Cat)]– complexes are in a ground state of S = 1/2, which results from the intramolecular antiferromagnetic interaction between CrIII(d3) and two semiquinonates. In addition, 3b and 4b have a contribution of the paramagnetic TMT-TTF˙+ (3b) and TMTSF˙+ (4b) cations. In all compounds weak intermolecular magnetic interactions were recognized from the decrease of the χmT values at low temperature.