Mechanism of reversible spin transition with a thermal hysteresis loop in [FeIII(qsal)2][Ni(dmise)2] • 2CH3CN: Selenium analogue of the precursor of an Fe(III) spin-crossover molecular conducting system

A novel Fe(III) spin-crossover complex, [Fe(qsal)(2)][Ni(dmise)(2)] center dot 2CH(3)CN 1 [qsalH = N-(8-quinolyl)-salicylaldimine, dmise = 4,5-dithiolato-1,3-dithiole-2-selone] was prepared. The magnetic susceptibility measurements revealed 1 exhibited a cooperative spin transition with a thermal hysteresis loop of 15 K. The high and the low temperature structures of 1 indicated three-dimensional intermolecular pi-pi interactions play a key role in the cooperative spin transition, accompanying a reversible molecular slipping of pi-dimer of Ni(dmise)(2) along the molecular long axis. The transfer integral calculation for 1 suggested the pi-dimer of Ni(dmise)(2) is in the spin singlet state. (C) 2008 Elsevier Ltd. All rights reserved.