ROY: Using the Method of Molecular Voronoi–Dirichlet Polyhedra to Examine the Fine Features of Conformational Polymorphism
В. Н. Сережкин, Lian Yu, Anton V. Savchenkov
Abstract
Crystal chemical analysis of 12 polymorphs of 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (ROY) (C12H9N3O2S)─the current record-holder of the number of structurally characterized polymorphic modifications─was carried out using the method of molecular Voronoi–Dirichlet (VD) polyhedra. Based on the k-Φ criterion, it was found that each of the 14 reported to-date independent ROY molecules has a unique conformation. A method for quantifying the significance of noncovalent interactions of various natures together with a new type of graph showing average partial contributions of single contacts of a given type to the values of integral parameters was proposed. The capabilities of the method of molecular VD polyhedra were successfully tested on the example of several forms of ROY with multiple structural solutions. The analysis showed that noncovalent interactions vary more between different forms of ROY than between different structural solutions of the same form. It was calculated that different structural solutions of the same form of ROY may feature up to five varying noncovalent contacts. The k-Φ criterion approved itself as a very sensitive parameter which can easily detect even the subtlest differences in atomic interactions strictly and quantitatively.