New four- and five-coordinated complexes of cobalt with sterically hindered o-iminobenzoquinone ligands:: synthesis and structure

New square planar Co-II(ISQ-iPr)(2) (1), Co-II(ISQ-Me)(2) (2) and five-coordinate Co-III(ISQ-Me)(2)Cl cobalt complexes (3) (ISQ-iPr = 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzosemiquinonate radical-anion, ISQ-Me = 4,6-di-tert-butyl-N-(2,6-dimethylphenyl)-o-iminobenzosemiquinonate radical-anion) have been prepared using different methods. Complexes 1 3 have been characterized by IR, UV-Vis, EPR spectroscopy. Molecular structures of 1 and 3 were determined using X-ray crystallography. It has been established from variable-temperature magnetic susceptibility measurements and X-band EPR spectroscopy that 1 and 2 possess an S = 1/2 ground state. In the complex molecules the unpaired electrons of o-iminobenzosemiquinonate radical ligands (S-rad = 1/2) are strongly coupled antiferromagnetically. The sterical hindrances of N-aryl in o-iminobenzo semiquition ate ligands prevent the formation of a hexacoordinate species. (C) 2004 Elsevier B.V. All rights reserved.