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 Fourier transform infrared spectroscopy on solid-state compounds. At room temperature the low-spin isomer is predominant for X = H and Cl complexes, whereas the X = OH complex shows a spin equilibrium and the CH3-substituted complex is present in its high-spin form. The spin-crossover 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 values found for the solution. Crystal water seems to favour the low-spin state of the OH complex.