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

Two novel bis-o-semiquinonato cobalt complexes Co(3,6-SQ)2L (1, L1 = 2,6-dimethyl-N-(pyridin-2-ylmethylene)benzenamine; 2, L2 = 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 L2 in the apical site. According to magnetic susceptibility measurements and spectroscopic studies, both complexes contain high-spin cobalt(II) (d7, 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.

Two new high-spin bis-o-semiqiunonato cobalt complexes containing nitrogen donor ligands were prepared. Complex with thiophene-containing ligand is pentacoordinated. The magnetic properties of both complexes have been investigated: Co(II) is high spin (S = 3/2) and the antiferromagnetic exchange interaction between paramagnetic ligands takes place; complexes demonstrate different metal–ligand magnetic exchange.Figure optionsDownload as PowerPoint slideHighlights
► Two new bis-o-semiquinonato cobalt complexes of Co(3,6-SQ)2L were prepared.
► Co(3,6-SQ)2L (ArN = CH-thiophene) is the first pentacoordinate cobalt(II) bis-semiquinolate.
► Complexes contain high-spin cobalt(II) and two radical-anionic o-semiquinones.
► Different magnetic behaviorswere found for complexes with ArN = CH-thiophene/pyridine.