Conformational Polymorphism: The Missing Phase of 1,1,2,2- Tetrachloroethane (Cl2HC-CHCl2)

PH. NEGRIER; M. BARRIO; J. LL. TAMARIT; D. MONDIEIG; M.J. ZURIAGA; S.C. PEREZ

CRYSTAL GROWTH & DESIGN

AMER CHEMICAL SOC

Lugar: Washington; Año: 2013 vol. 13 p. 2143 - 2148

1528-7483

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.