Theoretical and experimental investigation of novel iron(II)-based spin crossover compounds

Two novel spin crossover (SCO) compounds, namely [Fe(INMe)(pyN(4))]Br-2, and [Fe(IMMe)(pyN(4))](OTf)(2), where pyN(4) = 2,6-Bis(1',3'-diamino-2'methyl-prop-2'yl)pyridine, INMe = isonicotinic acid methyl ester, IMMe = N-methyl-imidazole, and OTf = triflate, are characterized here both from experimental and theoretical viewpoints. In particular, we apply various density functionals and basis sets to obtain optimized geometries for low- (LS) and high-spin (HS) states, vibrational spectra, LS-HS splittings, and temperature-dependent UV/vis spectra. While geometries and spectra are in good agreement with experimental data, the well-known spin pairing problem makes it difficult to compute accurate LS-HS splitting energies and enthalpies. Based on TD-DFT calculations, the capacity of the compounds for use as reversibly photo-switch able molecules is discussed. (C) 2007 Elsevier B.V. All rights reserved.