Influence of the ligand field on slow magnetization relaxation versus spin crossover in mononuclear cobalt complexes.

The electronic and magnetic properties of the complexes [Co(terpy)Cl2 ] (1), [Co(terpy)(NCS)2 ] (2), and Co(terpy)2 2 (3) were investigated. The coordination environment around Co(II) in 1 and 2 leads to a high-spin complex at low temperature and single-molecule magnet properties with multiple relaxation pathways. Changing the ligand field and geometry with an additional terpy ligand leads to spin-crossover behavior in 3 with a gradual transition from high spin to low spin.