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Vibrational Spectroscopy of Cyanide-Bridged, Iron(II) Spin-Crossover Coordination Polymers: Estimation of Vibrational Contributions to the Entropy Change Associated with the Spin Transition†
journal contribution
posted on 2002-08-29, 00:00 authored by Gábor Molnár, Virginie Niel, Ana B. Gaspar, José-A. Real, Antoine Zwick, Azzedine Bousseksou, John J. McGarveyA series of cyanide-bridged, iron(II) spin-crossover coordination polymers of formula Fe(py)2[M(CN)4] (M
= Pd or Pt; py = pyridine) and Fe(pz)[M(CN)4]·2H2O (M = Ni, Pd, or Pt; pz = pyrazine) have been studied
by recording the Raman and infrared (IR) spectra of their low-spin (LS) and high-spin (HS) forms in the
solid state. Spectral changes upon metal and ligand substitution were used to guide the assignment of vibrational
modes. Vibrational entropy changes upon spin transition were analyzed within the harmonic approximation.
The results confirm the major contribution of the Fe−ligand vibrations to the overall entropy change associated
with the spin transition (∼60%), butcontrary to expectationsreveal significant changes in other intra- and
intermolecular vibrations, of possible relevance to the high cooperativity of the spin transition.