The simultaneous crystallization of different polymorphs, i.e. concomitant polymorphism, is a phenomenon which, when properly recognized and studied, can provide useful information for a variety of disciplines. It is rare for ruthenium complexes, although it has been observed. In the synthesis of the ruthenium(II) complex chlorido(η6-p-cymene)(dimethyl 2,2'-bypyridine-4,5-dicarboxylate-κ2N,N')ruthenium(II) hexafluoridophosphate, [RuCl(C10H14)(C14H12N2O4)]PF6, concomitant polymorphs were crystallized under the same conditions. The colour of both crystals was orange, but the shapes, as well as the orientation of the p-cymene and methoxycarbonyl groups, were different. The crystal structures of both isomers show approximately the same bond lengths. In the asymmetric unit, there is one cation and one anion. Due to the absence of strong hydrogen bonds, only weak intermolecular interactions were observed. The Hirshfeld surface and two-dimensional fingerprint plots of both isomers satisfactorily explain the difference in the melting points.
Keywords: Hirshfeld surface; concomitant polymorphism; crystal structure; fingerprint plot; ruthenium complex.