Topology of spin-crossover polymers and mutual influence of ligands

Density functional quantum-chemical calculations for mononuclear fragments, [Fe-II(Pyim)(2)(bpy)](2+) [pyim = 2-(2-pyridyl)imidazole] and [Fe-II(aqin)(2)(bpy)](2+) (aqin = 8-aminoquinoline), of two recently synthesized spin-crossover compounds forming zigzag and linear coordination polymers, respectively, have been performed. The calculations suggest that the overall structure of the polymers is defined by the preference of the bidentate ligands for the cis or trans coordination mode, which in turn is determined by the character and efficiency of metal-ligand pi-interactions. This hypothesis is used to predict the structures of two other spin-transition compounds, which have not been studied by X-ray crystallography. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).