Fig. 1: Structural markers of Low Spin to High Spin phase transition at thermal equilibrium.
a [FeIII(3-MeO-SalEen)2]PF6 molecular lattices in Low Spin, LS (100 K, blue) and High Spin, HS (293 K, red) states, shown in the (a, c) plane. Ligands (in grey) are shown for the LS structure only. b X-ray diffraction (XRD) measurement on a single crystal: evolution on temperature, T, of the unit cell volume, V (T decreasing, plain black triangles, and T increasing, open circles) for extracting the thermal expansion parameters of the HS (red dotted line) and LS (blue dotted line) unit cell (Supplementary Note 120). Vertical black lines represent transition temperatures for T decreasing (Tdown) and T increasing (Tup). c–f Synchrotron x-ray powder diffraction on micro-crystals measured at ESRF, ID09 beamline: c Diffraction image measured at room temperature. d 1D powder patterns after azimuthal averaging of diffraction images (c) for the different temperature measured from 300 K to 100 K (upon cooling). e In yellow: temperature evolution of the magnetisation – temperature product MT as extracted from Superconducting Quantum Interface Device (SQUID) measurements; in grey: evolution of the HS fraction as extracted from the powder pattern refinement. Grey solid line is a guide for the eyes. f Temperature evolution of the mean unit cell volume as extracted from the powder pattern refinement. b, e and f: The vertical black line indicates transition temperature Tdown.
