Structural and spectroscopic characterizations of low-spin [Fe(4,4′-dimethyl-2,2′-bipyridine)3](NCS)2·3H2O prepared from high-spin iron(II) dithiocyanate tetrapyridine

Redetermination of the crystal structure of high-spin iron(II) dithiocyanate tetrapyridine [Fe(py)4(NCS)2] (1) (py=pyridine) at 85 and 291 K exhibits different unit cells when compared with that reported in 1967. An elongation in the compressed octahedron coordination environment around central ferrous ion is observed at low temperature, which can be verified by the DFT calculations of energy and dipole moments. 1 was then used as the Fe(II) source to synthesize [Fe(dmbpy)3](NCS)2·3H2O (2) (dmbpy=4,4′-dimethyl-2,2′-bipyridine). The X-ray diffraction studies of 2 reveal that six Fe–N bond distances are in the range 1.959(3)–1.971(3) Å suggesting the formation of the low-spin Fe(II) complex.