SUBSTITUENT-EFFECTS AND SOLVENT-EFFECTS ON THE STABILITY OF IRON(II)-4-X-2,6-BIS-(BENZIMIDAZOL-2'-YL)PHRIDINE COMPLEXES SHOWING SPIN-CROSSOVER IN SOLUTION

4-X-2,6-bis-(benzimidazol-2'-yl)pyridine (L = X-bzimpy; X = H, OH and Cl) acts as a tridentate when coordinated with iron(II) in solution. B oth, mono- and bis-species, [FeL](2+) and [FeL(2)](2+) are formed and the values of stability constants (logK(1) and logK(2)) were calculate d for these species in MeOH, 50% (v/v) PDC/MeOH and 10% (v/v) CHCl3/Me OH at 20 degrees C. The presence of electron-withdrawing substituents (Cl and OH) at 4-position on the pyridine ring of the ligand hardly in fluences the stability constants in contrast to a change in the spin-s tate to the high-spin (HS) state of the complexes. Studies of solvents influences on complexation equilibria reveal that the strong donor so lvent causes the dissociation and thereby decreases the values of stab ility constants. The value of magnetic moments (mu/mu B) for free iron (II) ion decreases with the formation of complex species of low-spin ( LS) state.