Spin coupling interactions in transition metal complexes containing radical o-semiquinone ligands.: A review

Transition metal complexes of o-semiquinone (SQ) ligands have been studied extensively over the past 25 years. A particularly interesting aspect of this coordination chemistry concerns magnetic interactions between paramagnetic metal ions and the radical anionic ligands. In this review we begin with a survey of relatively simple complexes consisting of a paramagnetic metal ion chelated by a single SQ ligand. Recent studies have revealed the importance of SQ-SQ coupling through diamagnetic metals, and complexes of this class are described in the second section of the review. Both interactions combine to account for the often complicated magnetic properties of complexes containing multiple SQ ligands chelated to a paramagnetic metal ion. Research on these complexes is surveyed in the third section with a concluding look toward polymeric SQ complexes. A review with 51 references.