Selection and discovery of polymorphs of platinum complexes facilitated by polymer-induced heteronucleation.

Polymer-induced heteronucleation was utilized for the selective crystallization of the color polymorphic platinum complexes Pt(bpy)Cl2 and Pt(phen)Cl2. Crystal structures of two polymorphs of Pt(phen)Cl2 were determined and reveal that, as in the case of Pt(bpy)Cl2, this compound has one form with Pt...Pt interactions (orange crystals) and another lacking these contacts (yellow crystals). Free energy measurements reveal that the polymorphs of Pt(bpy)Cl2 and Pt(phen)Cl2 without Pt...Pt interactions are more stable in both cases by 0.67(2) and 0.53(1) kJ/mol, respectively, and this finding is consistent with the principle of close packing. Furthermore, a search of the Cambridge Structural Database reveals that, for polymorphic platinum complexes, shorter intermolecular Pt...Pt interactions generally result in less dense structures.