A novel spin transition curve in [tris(2-picolylamine)Fe(II)]Cl2allyl solvate

The title compound exhibits a temperature dependent spin crossover with an intermediate plateau in the spin transition curve (STC) around 111K at an unusual high-spin concentration of about 30%.This is well below the plateau with a 50% concentration observed for the isomorphous ethanol solvate [1].We report here single crystal diffraction data collected at 200, 132, 111 and 94K.The systematic absences are consistent with B2 1 /c space group symmetry at 200 and 132K.At 111K, i.e. in the range of the plateau, a superstructure is observed.The consequential reflections violate the original B-centering and lead to P2 1 /c space group symmetry with a doubled unit cell volume.At 94K the original B2 1 /c symmetry is recovered, thus indicating a reentrant sequence of phase transformations [2].This observation shows that, as in the cases of the ethanol and 2propanol solvates [1,3], a plateau in the STC reflects the appearance of a new ordered structure.The plateau region is likely a result of the coupling of the spin conversion with the concurrent conformational ordering of the crystal architecture.

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