The spin-crossover complex [Fe(tpa)(NCS)(2)] - Investigated by synchrotron-radiation based spectroscopies

The temperature-Induced spin crossover of iron(II) in the [Fc(tpa)(NCS)(2)] complex has been investigated by nuclear forward scattering (NFS), nuclear inelastic scattering (NIS), extended X-ray absorption fine structure (EXAF S) spectroscopy, conventional Mossbauer spectroscopy (,MS) and by measureme nts of the magnetic susceptibility (SQUID). The various measurements consis tently show that the transition is complete and abrupt and exhibits a hyste resis between 102 and 110 K. The dependence of the hyperfine parameters of the high-spin (IIS) and of the low-spin (LS) phase on temperature is gradua l while the effective thickness (determined by the Lamb-Mossbauer factor f( LM)) shows a step at the transition temperature. This step could be identif ied clearly because the effective thickness is measured directly by NFS. Th e Lamb-Mossbauer factor, the Debye temperature and the mean-square displace ment of iron(II) could be determined for the HS and for the LS phase. When comparing the. NIS data with the results from density functional theory (DF T), the Fe-N stretching vibrations of both LS and HS phases could be unambi guously identified and the f(LM) could be factorized for both phases into a lattice and a molecular part. The structural information from EXAFS and DF T geometry optimization are in reasonable agreement.