Thermal-, Pressure- and Light-Induced Spin-Crossover Behaviour in the Two-Dimensional Hofmann-Like Coordination Polymer [Fe(3-Clpy)2Pd(CN)4]

The thermal spin-crossover behaviour, photoexcitation and subsequent relaxation, as well as the pressure-induced spincrossover behaviour at 298 K are discussed for the non-porous two-dimensional Hofmann-like coordination polymer [Fe(3-Clpy)(2)Pd(CN)(4)] (1). The title compound undergoes a two-step, cooperative thermal-induced SCO with critical temperatures T-c1(down arrow) = 159.6 K and T-c1(up arrow) = 164.5 K for the first step and T-c2(down arrow) = 141.4 K and T-c2(up arrow) = 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 Delta H-HL(p) = 22.01 kJ mol(-1) and 1'(p) = 7.47 kJ mol(-1), consistent with previous results.