Studies on a "Disappearing Polymorph": Thermal and Magnetic Characterization of α-p-NCC6F4CNSSN•.

The α-and β-phases of the thiazyl radicalp-NCC6F4CNSSN•(<bold>1</bold>) can be selectively prepared by careful control of the sublimation conditions, with the α-phase crystallizing preferentially when the substrate temperature is maintained below −10 °C, whereas the β-phase is isolated when the substrate temperature is maintained at or above ambient temperature. Differential scanning calorimatry studies reveal that the α-phase converts to the β-phase upon warming over the range 111–117 °C (ΔH= +4 kJ·mol–1) via a melt–recrystallization process, with the β-phase itself melting at 167–170 °C (ΔH fus= 27 kJ·mol–1). IR and Raman spectroscopy can be used to clearly discriminate between<bold>1α</bold>and<bold>1β</bold>. The α-phase shows a broad maximum in the magnetic susceptibility around 8 K that, coupled with a broad maximum in the heat capacity, is indicative of short-range order. Some field dependence of the susceptibility below 3 K is observed, but the lack of features in the ac susceptibility,MvsHplots, or heat capacity mitigates against long-range order in<bold>1α</bold>. [ABSTRACT FROM AUTHOR]