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Issue 10, 2011
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Polymorphism of 5-(pyridin-2-ylmethylene)-3-phenyl-2-methylthio-3,5-dihydro-4H-imidazole-4-one

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The title compound, C16H13N3OS (1), exists in three polymorphic forms. Crystalline 1 undergoes an enantiotropic, first-order, k2 phase transition at 262.9(5) K with ΔH = 0.3(1) kJ mol−1. Upon cooling below the transition temperature, the high temperature orthorhombic polymorph (Form I, space groupPbcm) transforms into a low temperature orthorhombic polymorph (Form II, space groupPbca) with a unit cell twice the size of that of the Form I. A molten 1 can be cooled in a controlled fashion to generate a monoclinic Form III of 1 with the unit cell size similar to that of Form I. Metastable Form III, once isolated, is indefinitely stable between 100 K and its melting point of 466 K. If crystals of Form III are in contact with seed crystals of Form I, a monotropic t2 first-order Form III → Form I phase transition occurs upon heating with the onset between 420 and 448 K and ΔH = −1.7(4) kJ mol−1. The most substantial differences among the molecular geometries of 1 in Forms IIII are observed in the position and tilt of the phenyl ring relative to the rest of the molecule. The packing in Form III is very different from those in the other polymorphs. DFT molecular geometry optimizations produce the following order of stable molecule configurations: Form II (most stable), Form I (0.50 kJ mol−1), Form III (2.81 kJ mol−1).

Graphical abstract: Polymorphism of 5-(pyridin-2-ylmethylene)-3-phenyl-2-methylthio-3,5-dihydro-4H-imidazole-4-one

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Article information

18 Jan 2011
12 Feb 2011
First published
10 Mar 2011

CrystEngComm, 2011,13, 3444-3450
Article type

Polymorphism of 5-(pyridin-2-ylmethylene)-3-phenyl-2-methylthio-3,5-dihydro-4H-imidazole-4-one

I. A. Guzei, E. M. Gunn, L. C. Spencer, J. M. Schomaker and J. W. Rigoli, CrystEngComm, 2011, 13, 3444
DOI: 10.1039/C1CE05098B

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