Tuning the spin crossover above room temperature:: iron(II) complexes of substituted and deprotonated 2,6-bis(benzimidazol-2-yl)pyridine

The complex [Fe(tzimpy)(2)](ClO4)(2) . 2H(2)O (tzimpy = 2,4,6-tris-(benzimidazol-2-yl)pyridine) shows an abrupt spin crossover (S = 0-2 transition) above room temperature centered at T-c = 323 K with a hysteresis width of AT = 35 K. The neutral iron(II) complex with deprotonated bzimpy ligands (bzimpy = 2,6-bis(benzimidazol-2-yl)pyridine) exhibits a gradual spin transition on the first heating with T, = 424 K. There are irreversible changes between T = 503 and 523 K: the liberation of the crystal water, the color change (blue-green) followed by a structure change. Next thermal cycles are reproducible though, heating/cooling paths are different from the first heating. (C) 2004 Elsevier B.V. All rights reserved.