First Cobalt(II) Spin Crossover Compound with N(4)S(2)-Donorset

Herein we report the synthesis and characterization of a novel bis-tridentate 1,3,4-thiadiazole ligand (L = 2,5-bis[(2-pyridylmethyl)thio]methyl-1,3,4-thiadiazole). Two new mononuclear complexes of the type [M(II)(L)(2)](ClO(4))(2) (with M = Fe(II) (C1) and Co(II) (C2)) have been synthesized, containing the new ligand (L). In both complexes the metal centers are coordinated by an N(4)S(2)-donorset and each of the two ligands is donating to the metal ion with just one of the tridentate pockets. The iron(II) complex (C1) is in the low spin [LS] state below room temperature and shows an increase in the magnetic moment only above 300 K. In contrast, the cobalt(II) complex (C2) shows a gradual spin crossover (SCO) with T(1/2) = 175 K. To our knowledge, this is the first cobalt(II) SCO complex with an N(4)S(2)-coordination.