Transition metal complexes based on pyridine ligand containing both bis(2-pyridyl) and 1,3-dithiole-2-ylidene units: Syntheses, structures, and magnetic studies

Two new mononuclear spin-crossover iron(II) complexes, [FeL2(NCS)2] · H2O (1) and [FeL2(NCSe)2] (2), have been synthesized from the reaction of the versatile ligand 4,5-bis(2-cyanoethylthio)-2-bis(2-pyridyl)methylene-1,3-dithiole (L), Fe(ClO4)2, and KNCX (X = S/Se). Reactions of L with CuII or CoII salts afford one mononuclear complex [CuL(hfac)2] · CH3OH (hfac = hexafluoroacetylacetonate) (3), one dinuclear complex [(CuLCl)2(μ-Cl)2] · CH3OH (4), and two 1D chain species, [CuL2]n(BF4)2n (5) and [CoL2]n(ClO4)2n · 2nCH2Cl2 (6). The crystal structures of complexes 1 and 3–6 have been determined by X-ray crystallography. Short intermolecular S⋯S contacts between neighboring 1D arrays are observed in 5 and 6, which lead to the formation of the 2D structure. The magnetic properties are studied, and antiferromagnetic couplings between the CuII centers across the chloride bridges have been found in 4 (J = 2.04 cm–1). Spin-crossover behaviors between high and low spin states are observed at T1/2 = 80 K for 1 and T1/2 = 300 K for 2, respectively.