6533b833fe1ef96bd129b610

RESEARCH PRODUCT

Two-step spin crossover behaviour in the chiral one-dimensional coordination polymer [Fe(HAT)(NCS)2]∞

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Solvated and unsolvated forms of the complex [Fe(HAT)(NCS)2]∞·(nMeOH) (1) (n = 1.5, 0; HAT = 1,4,5,8,9,12-hexaazatriphenylene) were prepared. The structure of 1·(1.5MeOH), measured at 120 K, showed that this system crystallizes in the homochiral P43 tetragonal space group. The solid is constituted of stacks of one-dimensional coordination polymers running along c-axis. All the FeII centres have the same Λ or Δ conformation and are in the LS state at 120 K. In the range of temperatures 10–300 K the magnetic properties of 1·(1.5MeOH) shows the occurrence of reversible spin crossover behaviour. However, above ca. 310 K complete desolvation of 1·(1.5MeOH) to give 1 was observed from crystal structure analysis, magnetic behaviour and thermal analysis. Compound 1 displays a two-step spin crossover behaviour characterised by a plateau 60 K wide. Simulation of the two-step behaviour in the frame of the regular solutions theory afforded, respectively, the critical temperatures (Tci), the interaction parameters (Γi), and the enthalpy (ΔHi) and entropy (ΔSi) variations for steps i = 1 and 2: Tc1(Tc2) = 172 (358) K, Γ1(Γ2) = 1.6 (3.0) kJ mol−1, ΔH1(ΔH2) = 5.7 (18.3) kJ mol−1 and ΔS1(ΔS2) = 33.4 (51.0) J K mol−1.