New high-spin bis-o-semiquinonato cobalt(II) complexes with neutral donor ligands

Two novel bis-o-semiquinonato cobalt complexes Co(3,6-SQ)(2)L (1, L(1) = 2,6-dimethyl-N-(pyridin-2-ylmethylene)benzenamine; 2. L(2) = 2,6-dimethyl-N-(thiophen-2-ylmethylene)benzenamine: 3,6-SQ is 3,6-di-tert-butyl-o-benzosemiquinonato radical-anion) were synthesized. According to X-ray analysis, complex 2 adopts square pyramidal geometry with N-coordinated neutral ligand L(2) in the apical site. According to magnetic susceptibility measurements and spectroscopic studies, both complexes contain high-spin cobalt(II) (d(7), S = 3/2) and two radical-anionic o-semiquinonato ligands. There is antiferromagnetic metal-ligand and ligand-ligand coupling in 1, while complex 2 demonstrates weak antiferromagnetic ligand-ligand coupling at low temperature and ferromagnetic metal-ligand exchange at 150-300 K. (C) 2011 Elsevier B.V. All rights reserved.