Thermal-, pressure- and light-induced spin-crossover behviour in the two-dimensional Hofman-like coordination polymer [Fe(3-Clpy)2Pd(CN)4]
Résumé
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.