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

The reaction of tris-tetrahalogeno-o-benzosemiquinonate chromium(III) complexes, [Cr-III(X(4)SQ)(3)] (X=Cl 1a or Br 1b), with bis(cyclopentadienyl) cobalt [(CoCp2)-Cp-II], tetramethyltetraselenafulvalene (TMTSF) and tetrakis(methylsulfanyl)tetrathiafulvalene (TMT-TTF) afforded four charge-transfer compounds, [(CoCp2)-Cp-III][Cr-III(X(4)SQ)(2)(X(4)Cat)] (X=Cl 2a or Br 2b), [TMT-TTF][Cr-III(Br(4)SQ)(2)(Br(4)Cat)] 3b and [TMTSF][Cr-III(Br(4)SQ)(2)(Br(4)Cat)] 4b, where Cat is catecholate. The paramagnetic [Cr-III(X(4)SQ)(2)(X(4)Cat)](-) complexes are commonly formed by cocrystallization with a diamagnetic [(CoCp2)-Cp-III](+) cation for 2a . C6H6 and 2b, and paramagnetic TMT-TTF.+ and TMTSF.+ cations for 3b . C6H5CH3 and 4b . 2CH(2)Cl(2), respectively. The one-electron reduced complexes, [Cr-III(X(4)SQ)(2)(X(4)Cat)](-), 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 . 2CH(2)Cl(2) 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 [Cr-III(X(4)SQ)(2)(X(4)Cat)](-) complexes are in a ground state of S=1/2, which results from the intramolecular antiferromagnetic interaction between Cr-III(d(3)) 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 chi(m)T values at low temperature.