Cobalt and Iron Cyano Benzene Bis(Dithiolene) Complexes.

New iron and cobalt bis(dithiolene) complexes [M(3cbdt)₂] (3cbdt = 3-cyanobenzene-1,2-dithiolate) were prepared as tetraphenylphosphonium (Ph₄P⁺) salts for Fe in the monoanionic state and for Co in both the dianionic and monoanionic states: (Ph₄P)₂[Fe(III)(3cbdt)₂]₂ (1); (Ph₄P)₂[Co(III)(3cbdt)₂]₂ (2); (Ph₄P)₂[Co(II)(3cbdt)₂] (3). These compounds were characterized by single-crystal X-ray diffraction, cyclic voltammetry, EPR, and static magnetic susceptibility. Their properties are discussed in comparison with the corresponding complexes based on the isomer ligand 4-cyanobenzene-1,2-dithiolate (4cbdt) and 4,5-cyanobenzene-1,2-dithiolate (dcbdt), previously described by us. The Fe(III) and the Co(III) compounds (1 and 2) are isostructural, crystallizing in the triclinic P 1 ¯ space group, with cis [M(III)(3cbdt)₂] complexes dimerized in a trans fashion, and the transition metal (M = Fe, Co) has a distorted 4+1 square pyramidal coordination geometry. The Co(II) compound (3) crystallizes in the triclinic P 1 ¯ space group, with the unit cell containing one cis and three trans inequivalent [Co(II)(3cbdt)₂] complexes with the transition metal (Co) and having a square planar coordination geometry. The Fe(III) complex (1) is EPR-silent, and the static magnetic susceptibility shows a temperature dependence typical of dimers of antiferromagnetically coupled S = 3/2 spins with −J/k_B = 233.6 K and g = 1.8. Static magnetic susceptibility measurements of compound (3) show that this Co(II) complex is paramagnetic, corresponding to an S = ½ state with g = 2, in agreement with EPR spectra showing in solid state a hyperfine structure typical of the I(⁵⁹Co) = 7/2. Static susceptibility measurements of Co(III) complex (2) showed an increase in the paramagnetic susceptibility upon warming above 100 K, which is consistent with strong AFM coupling between dimerized S = 1 units with a constant −J/k_B ~1286 K. [ABSTRACT FROM AUTHOR]