화학공학소재연구정보센터
Thermochimica Acta, Vol.388, No.1-2, 401-406, 2002
Formation constants and thermodynamic properties of the spin-crossover Fe(II)-2,6-bis-(benzimidazol-2'-yl)pyridine complex
The tridentate ligand, 2,6-bis-(benzimidazol-2-yl)pyridine (bzimpy) coordinates to iron(II) and forms the mono- and bis-complexes, [FeLS3](2+) (S = solvent) and [FeL2](2+) in 50% (v/v) PC/MeOH (PC = propanedilo-1,2-carbonate). The complexes are characterized by observed metal-to-ligand charge transfer (MLCT) bands with absorption maximum at 500.0 +/- 5.0 nm (epsilon(max) = 200-700 l mol(-1) cm(-1)) for [FeLS3](2+) and at 555.0 +/- 1.0 nm (epsilon(max) = 5100-7500 l mol(-1) cm(-1)) for [FeL2](2+). The complexation equilibria are studied at an extended temperature range of 4, 13, 20 and 32 +/- 1 degreesC in 50% (v/v) PC/MeOH. The values of formation constants (log(10) beta(2) = 10.90-11.47) are calculated and found to decrease with increasing temperature. The thermodynamic parameters (DeltaH and DeltaS) for complexation equilibria are 50.52 kJ mol(-1) and 43.28 J mol(-1) K-1, respectively. Study at low temperature (4 degreesC) reveals the likely formation of a tris-complex, [FeL3 ](2+) in addition to [FeLS3](2+) and [FeL2](2+) in solution.