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The effect of pressure on the spin-transition properties of the 2D coordination polymer {Fe(phpy)2[Ni(CN)4]} is reported. The study has been carried out by means of variable-temperature (10-310 K) magnetic susceptibility measurements at applied pressures of 105 Pa to 1.0 GPa and spectroscopic studies in the visible region at room temperature (105 Pa-3.0 GPa). As the pressure is increased, the characteristic temperature of the spin transition is displaced to higher temperatures and the thermal hysteresis loop disappears. A cooperative first-order spin transition characterized by a piezo-hysteresis loop about 0.3 GPa wide was observed at 293 K. [ABSTRACT FROM AUTHOR]

The thermal spin-crossover behaviour, photoexcitation and subsequent relaxation, as well as the pressure-induced spin-crossover behaviour at 298 K are discussed for the non-porous two-dimensional Hofmann-like coordination polymer [Fe(3-Clpy)2Pd(CN)4] ( 1). The title compound undergoes a two-step, cooperative thermal-induced SCO with critical temperatures Tc1↓ = 159.6 K and Tc1↑ = 164.5 K for the first step and Tc2↓ = 141.4 K and Tc2↑ = 148.4 K for the second step. Irradiation of the low-spin state with green light (514 nm) at 10 K induced the photoexcitation of around 60 % of the iron(II) centres to the high-spin state (LIESST effect). The subsequent cooperative relaxation processes were recorded at several temperatures and analysed. The effect of cooperativity on the photoexcitation was investigated by the LITH (light-induced thermal hysteresis) procedure. At 300 K, the coordination polymer 1 underwent a cooperative spin-crossover transition at around 0.6 GPa. The thermodynamic analysis of the pressure-induced SCO transition afforded the enthalpy and cooperativity parameters Δ HHL( p) = 22.01 kJ mol-1 and Γ( p) = 7.47 kJ mol-1, consistent with previous results. [ABSTRACT FROM AUTHOR]