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

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Abstract

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 ΔHHL(p) = 22.01 kJ mol–1 and Γ(p) = 7.47 kJ mol–1, consistent with previous results.

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