Pressure-induced changes of the vibrational modes of spin-crossover complexes studied by nuclear resonance scattering of synchrotron radiation

Nuclear inelastic scattering (NIS) spectra were recorded for the spin-crossover complexes STP and ETP (STP [Fe(1,1,1-tris{[N-(2-pyridylmethyl)-N- methylamino]methyl}-ethane)](ClO₄)₂ and ETP [Fe(1,1,1-tris{[N-(2-pyridylmethyl)-N-methylamino]methyl}-butane)](ClO ₄)₂) at 30 K and at room temperature and also at ambient pressure and applied pressure (up to 2.6 GPa). Spin transition from the high-spin (HS) to the low-spin (LS) state was observed by lowering temperature and also by applying pressure at room temperature and has been assigned to the hardening of iron-bond stretching modes due to the smaller volume in the LS isomer.