Conformational polymorphism: The missing phase of 1,1,2,2-tetrachloroethane (Cl2HC-CHCl2)
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Halogenoethane derivatives are known to exhibit different polymorphs involving a different translational, orientational, and conformational order. The 1,1,2,2- tetrachloroethane (Cl2HC−CHCl2) exhibits a normal pressure orthorhombic phase β (space group P212121 with Z = 8 and Z′ = 2), formed by molecules with one of the two gauche conformations. At high pressure, the stable polymorph is known to be monoclinic (space group P21/c, with Z = 2 and Z′ = 0.5), phase α, in which only the trans conformer appears. In this work, we demonstrate the existence of a normal pressure metastable polymorph, phase γ, for which the two gauche conformers show up in the asymmetric unit of a monoclinic (space group P21/c with Z = 8 and Z′ = 2) structure. The new phase γ is obtained by recrystallization upon heating the glass obtained after quench of the melt. It displays shorter type II Cl···Cl contacts than the high-pressure phase α due to attractive and directional interactions.
CitationDel Barrio, M. [et al.]. Conformational polymorphism: The missing phase of 1,1,2,2-tetrachloroethane (Cl2HC-CHCl2). "Crystal growth and design", Maig 2013, vol. 13, núm. 5, p. 2143-2148.