Synthesis, solid-state structures, and EPR spectroscopic studies on polycrystalline and single-crystal samples of α-diimine cobalt(II) complexes

Cobalt compounds of the general formula [CoX₂(α-diimine)], where X = Cl or I and the α-diimines are 1,4-diaryl-2,3-dimethyl-1,4- diaza-1,3-butadiene (Ar-DAB) and bis(aryl)-acenaphthenequinonediimine (Ar-BIAN) were synthesized by the direct reaction of the anhydrous cobalt salts CoCl ₂ or CoI₂ and the corresponding α-diimine ligand in dried CH₂Cl₂. The synthesized compounds are [Co(Ph-DAB)Cl₂] (1a), [Co(o,o′,p-Me₃C ₆H₂-DAB)Cl₂] (1b), and [Co(o,o′-iPr ₂C₆H₃-DAB)Cl₂] (1c) with the ligands Ar-DAB, and also [Co(o,o′,p-Me₃C₆H ₂-BIAN)I₂] (2′b) with the ligand Ar-BIAN. The crystal structures of all the compounds were solved by single-crystal X-ray diffraction. In all cases the cobalt atom is in a distorted tetrahedron, which is built up of two halide atoms and two nitrogen atoms of the α-diimine ligand. X-band EPR measurements of polycrystalline samples performed on compounds 1b, 1c, and 2′b indicate a high-spin Co^II ion (S = 3/2) in an axially distorted environment. Single-crystal EPR experiments on compounds 1b and 1c allowed us to evaluate the orientation of the g tensor in the molecular frame.