Substituent Effects on the Spin-Transition Temperature in Complexes with   Tris(pyrazolyl) Ligands
  Iron (II) complexes with substituted tris(pyrazolyl) ligands, which exhibit a thermally driven transition from a low-spin state at low temperatures to a high-spin state at elevated temperatures, have been studied by M\"ossbauer spectroscopy and magnetic susceptibility measurements. From the observed spectra the molar high-spin fraction and the transition temperature have been extracted. All substituents, except for bromine, lead to a decrease of the transition temperature. Density functional calculations have been carried out to compare the experimentally observed shifts of the transition temperature with those derived from theory. 
Hauke Paulsen, Lars Duelund, Axel Zimmermann, Fr\'ed\'eric Averseng,   Michael Gerdan, Heiner Winkler, Hans Toftlund, and Al...
physics.chem-ph