VIBRATIONAL SPECTROSCOPY ON IRON(II) SPIN-CROSSOVER COMPLEXES WITH 4-SUBSTITUTED 2,6-BIS(BENZIMIDAZOL-2'-YL)PYRIDINE

Substituent and temperature effects on the spin-crossover behaviour of cationic complexes of iron(II)-X-2,6-bis(benzimidazol-2'-yl)pyridine (X = H, OH, Cl and CH3) were investigated by means of UV-visible and F ourier transform infrared spectroscopy on solid-state compounds. At ro om temperature the low-spin isomer is predominant for X = H and Cl com plexes, whereas the X = OH complex shows a spin equilibrium and the CH 3-substituted complex is present in its high-spin form. The spin-cross over behaviour for the Cl-substituted species corresponds to a Delta H -SC of about 0.5 kJ mol(-1) which is much lower than the respective va lues found for the solution. Crystal water seems to favour the low-spi n state of the OH complex.