Calorimetric investigations of phase transitions in which electrons are directly involved

Synergic on/off Photoswitching Spin State and Magnetic Coupling between Spin Crossover Centers

“…In general, the entropy change arising from spin crossover consists of contributions from the difference in spin multiplicity, orbital degeneracy, and density of vibration modes. The entropy gain from the difference in spin multiplicity for two Fe II centers ( S HS = 2 for Fe II HS and S LS = 0 for Fe II LS ) is 2 R ln­[(2 S HS + 1)/(2 S LS + 1)] = R ln 25 (= 26.76 J K –1 mol –1 ), where R is the gas constant. − The entropy contribution from the change in the orbital degeneracies could be neglectful because the orbital degeneracy has been lifted by the structural distortion to give a nondegenerate orbital, which are also observed in other SCO complexes. , The excess entropy beyond the contribution from the spin multiplicity mainly arises from intramolecular vibrations corresponding to the significant changes in Fe–N stretching and N–Fe–N deformation vibration as described in the crystal structure, Raman and IR spectra. These results suggest that thermally induced spin crossover from LS to HS state is an entropy-driven process …”

“…39−41 The entropy contribution from the change in the orbital degeneracies could be neglectful because the orbital degeneracy has been lifted by the structural distortion to give a nondegenerate orbital, which are also observed in other SCO complexes. 39,42 The excess entropy beyond the contribution from the spin multiplicity mainly arises from intramolecular vibrations corresponding to the significant changes in Fe−N stretching and N−Fe−N deformation vibration as described in the crystal structure, Raman and IR spectra. These results suggest that thermally induced spin crossover from LS to HS state is an entropy-driven process.…”

Calorimetric Investigation of Phase Transitions Occurring in Molecule-Based Magnets

“…However, descriptions about how to interpret experimental results are scarce or limited to very classical examples, if any. Therefore, a brief description will be made, at first, about what kinds of microscopic and macroscopic information are derived from actual calorimetry. − …”

“…Complexes showing spin crossover phenomena are typical molecule-based magnets, because the magnetic properties dramatically change through the LS to HS transition. − However, the calorimetric studies have already been summarized by one of the authors (M.S.) in review articles, − and thus only a few topics will be picked up here.…”

Magnetostructural Relationships For Fe(III) Spin Crossover Complexes

“…These thermodynamic data can be measured by calorimetry (SORAI, 2002) but they are available also from an analysis of magnetic data such as temperature dependence of the magnetic susceptibility (BOČA et al, 2003;PAVLIK et al, 2013).…”