SPIN-CROSSOVER OF [Fe(Cl-BZIMPY)2](ClO4)2INDUCED BY DEPROTONATION

The ligand 4-Cl-2,6-bis(benzimidazol-2′-yl)-pyridine(Cl-bzimpy;H2L) acts as a bidentate when coordinated with transition metal ions and the complex [Fe(Cl-bzimpy)2](ClO4)2 was isolated as a solid. The protonation constants (logK). The free ligand and the complex were evaluated in 30:70 (v/v) H2O:EtOH at room temperature and ionic strength of 0.13M (KCl). Coordination of the ligand to the metal ion leads to an increase of the acidity of the imino-hydrogen of the benzimidazole group. Deprotonation leads to a change in the spin-state (to the low-spin state; HS → LS transition) of the complex associated with a decrease in the spin-crossover equilibrium constant (Ksc). An opposite shift of spin-state is observed when HClO4 is added to the complex solution, thus showing the reversibility of the process.