Structural origin of the gradual spin transition in a mononuclear iron(II) complex

Variable temperature single crystal X-ray diffraction and SQUID magnetometry experiments have revealed a gradual spin transition in [FeII(L)](ClO4)2 (where L=1,4,7-tris(2-aminophenyl)-1,4,7-triazacyclononane), centred around room temperature. The gradual nature of the spin transition has been attributed to the lack of significant intermolecular interactions between iron centres and the propensity of the counter ions to accommodate the internal strain in the crystal caused by spin crossover.

► Extremely gradual spin crossover observed in molecular Fe(II) complex.
► Spin transition characterised with structural and magnetic techniques.
► Counter ions accommodate the internal strain caused by SCO—lack of cooperativity.