Synthesis, Luminescence, and Structure of a Polymorphic Polyfluorinated Diiodoplatinum(II) Diimine Complex

PtI₂(5,5'-bis(HCF₂CH₂OCH₂)-2,2'-bpy)], 55-2FH-PtI, is the first example of a substituted fluorinated diiodoplatinum diimine complex that exhibits polymorphism. The complex, upon recrystallization, forms two different polymorphs, denoted as α and β forms. The luminescence of the α and β forms are the same in glassy solution at 77 K; however, in the solid state, they differ significantly. The major difference between them lies in the solid-state packing of the crystalline structure. The α form is a square planar polyfluorinated PtI₂-containing complex. Its extended herringbone structure consists of two neighboring stacked bipyridyl planes that do not overlap. The α form emits stronger than its parent molecule, [PtI₂bpy], and much stronger than the β polymorph. The β form has a slight tetrahedral distortion about the metal center that ultimately changes the geometry of the complex and decreases the d-orbital splitting from square planar. Furthermore, overlapping bipyridine rings in the extended structure of the β form quench the emission thus resulting in a lower energy emission. Additionally, the β form shows only one type of C-H···O intermolecular stacking interaction that can cause the moderate distortion of the metal core.