⁵⁷Fe Mossbauer spectroscopic and magnetic study of a spin-crossover polymer complex, Fe(3-chloropyridine)₂Ni(CN)₄

The coordination polymer Fe(3-chloropyridine)₂Ni(CN)₄ (2) has been prepared by a method similar to that for Fe(pyridine)₂Ni(CN)₄ (1). The complex (2) has been characterized by ⁵⁷Fe Mossbauer spectroscopy and a SQUID technique. ⁵⁷Fe Mossbauer and magnetic susceptibility data show that complex (2) exhibits spin-crossover behavior. The spin transition of (2) occurs between 120 and 80 K with very small hysteresis or without hysteresis. The temperature range of the spin transition in (2) is lower than that in (1). A residual high spin iron(II) fraction is observed at low temperatures in (2), being different from (1). SQUID data also show that samples treated differently yield different spin transition curves.