The Nature of Conformational Polymorphism in the Crystals of Ph3Sb(O2CCH2–CH=CH2)2

Abstract

Crystallization of the Ph₃Sb(O₂CCH₂−CH=CH₂)₂ complex upon fast solvent (benzene) evaporation gives monoclinic crystals (I), whereas in the case of slow evaporation, triclinic crystals are formed (II). Also, monoclinic crystals are spontaneously transformed into triclinic crystals within 6 months. It was shown that the presence of voids near one carboxylate ligand in the monoclinic phase of Ph₃Sb-(O₂CCH₂−CH=CH₂)₂ decreases the energy of intermolecular interactions and, as a consequence, leads to a conformational transition with a noticeable decrease in the crystal lattice energy. Thus, the presence of voids in the monoclinic phase crystal allows the formation of a thermodynamically more favorable conformation of the molecule in the crystal. Several structural models were determined for the Ph₃Sb(O₂CCH₂−CH=CH₂)₂ complex (CIF files no. 1887561 (I_IAM), model of non-interacting atoms; 1887562 (I), multipole model; 1887563 (II_IAM), model of non-interacting atoms; 1887564 (II), multipole model).