Temperature- and pressure-dependent structural study of {Fe(pmd)2[Ag(CN)2]2}n spin-crossover compound by neutron Laue diffraction

The effect of pressure (up to 0.17 GPa) on the spin-crossover compound {Fe(pmd)(2)[Ag(CN)(2)](2)}(n) [orthorhombic isomer (II), pmd = pyrimidine] has been investigated by temperature-and pressure-dependent neutron Laue diffraction and magnetometry. The cooperative high-spin <-> low-spin transition, centred at ca 180 K at ambient pressure, is shifted to higher temperatures as pressure is applied, showing a moderate sensitivity of the compound to pressure, since the spin transition is displaced by ca 140 K GPa(-1). The space-group symmetry (orthorhombic Pccn) remains unchanged over the pressure-temperature (P-T) range studied. The main structural consequence of the high-spin to low-spin transition is the contraction of the distorted octahedral [FeN6] chromophores, being more marked in the axial positions (occupied by the pmd units), than in the equatorial positions (occupied by four [Ag(CN)(2)](-) bridging ligands).