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 (<b>1</b>); (Ph₄P)₂[Co(III)(3cbdt)₂]₂ (<b>2</b>); (Ph₄P)₂[Co(II)(3cbdt)₂] (<b>3</b>). 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 (<b>1</b> and <b>2</b>) are isostructural, crystallizing in the triclinic <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>P</mi><mover accent="false"><mrow><mn>1</mn></mrow><mo>¯</mo></mover></mrow></semantics></math></inline-formula> 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 (<b>3</b>) crystallizes in the triclinic <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>P</mi><mover accent="false"><mrow><mn>1</mn></mrow><mo>¯</mo></mover></mrow></semantics></math></inline-formula> 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 (<b>1</b>) is EPR-silent, and the static magnetic susceptibility shows a temperature dependence typical of dimers of antiferromagnetically coupled <i>S</i> = 3/2 spins with −<i>J</i>/<i>k_B</i> = 233.6 K and <i>g</i> = 1.8. Static magnetic susceptibility measurements of compound (<b>3</b>) show that this Co(II) complex is paramagnetic, corresponding to an <i>S</i> = ½ state with <i>g</i> = 2, in agreement with EPR spectra showing in solid state a hyperfine structure typical of the <i>I(</i>⁵⁹Co) = 7/2. Static susceptibility measurements of Co(III) complex (<b>2</b>) showed an increase in the paramagnetic susceptibility upon warming above 100 K, which is consistent with strong AFM coupling between dimerized <i>S</i> = 1 units with a constant −<i>J</i>/<i>k_B</i> ~1286 K.