High-spin low-spin transition
  Temperature dependent nuclear inelastic-scattering (NIS) of synchrotron radiation was applied to investigate both spin states of the spin-crossover complex [Fe(tpa)(NCS)(2)] (tpa = tris(2-pyridylmethyl)amine). A remarkable increase of the iron-ligand bond stretching upon spin crossover has unambiguously been identified by comparing the measured NIS spectra with theoretical simulations based on density-functional calculations. 
H. Gr\"unsteudel and H. Paulsen and H. Winkler and A. X. Trautwein and   H. Toftlund
physics.chem-ph