The role of dispersion type metal⋯π interaction in the enantiotropic phase transition of two polymorphs of tris-(thienyl)bismuthine

Abstract

Two polymorphs of tris(thienyl)bismuthine Bi(2-C₄H₃S)₃ (1) were isolated upon crystallization from n-hexane at different temperatures. The high temperature form 1-HT crystallized at 269 K in the trigonal space group R, whereas the low temperature form 1-LT crystallized at 245 K in the triclinic space group P. An enantiotropic phase transition was observed at 250 K showing a transition energy of 1.4 kJ mol⁻¹. Both polymorphs reveal the formation of centrosymmetric dimers that are based on London dispersion type bismuth⋯π heteroarene interactions. These primary building units show additional dispersion type interactions between neighbouring dimers and as a result 2D networks are formed. DFT calculations on the model systems BiX₃⋯π thiophene (X = Cl, Me) verify the hypothesis of a soft and shallow binding potential of the London dispersion type bismuth⋯π heteroarene interaction, providing an explanation for the reversibility of the phase transition.