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.