Mitsuaki Suzuki, Y. Maeda, Motoko Akita
Oct 21, 2014
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Journal
Crystal Growth & Design
Abstract
Variable-temperature single-crystal X-ray diffraction analyses of 1,3-diethyl-spiro[imidazolidine-2,2′-[2H]indene]-1′,3′-dione (1) were performed at low temperatures. The temperature dependence of the cell parameters exhibited a discontinuous change between 158 and 153 K, indicating the existence of a phase transition and hence the occurrence of two polymorphs, I and II, which was also confirmed by DSC analysis: reversible exothermic and endothermic peaks with ΔH = 2.1 kJ mol–1 were observed in the cooling and heating processes, respectively. The molecular packing in I and II at 200 and 90 K, respectively, remained essentially unchanged, retaining the space group Pnma. I and II are conformationally isomorphic crystals, including two crystallographically independent molecules, A and B, with different conformations in a 1:2 ratio. Upon the phase transition from I to II with decreasing temperature, the dynamic disorder of the imidazolidine ring of A in I, which interconverts between quasi-half-chair conforma...