Two-step spin crossover in the mononuclear iron(II) complex [Fe(II)(L)(2)(NCS)(2)] (L = 2,5-di-(2-pyridyl)-1,3,4-thiadiazole).

The first iron(ii) complex of 2,5-di-(2-pyridyl)-1,3,4-thiadiazole (L), namely [Fe(II)(L)(2)(NCS)(2)], has been synthesised and studied by magnetic susceptibility measurements, Mössbauer spectroscopy and X-ray diffraction. It has been found to undergo thermally-induced spin crossover featuring two well-separated, abrupt steps at T(1/2)(1) = 167 K and T(1/2)(2) = 112 K.