Novel (2,2′-Bipyridine)PtBr₂ Packing Polymorphic Form Produced in Chloroform–Ionic Liquid Dispersion

Ionic liquids, composed fully of charged particles, have unique physical properties influencing complex formation and crystal growth. In the presence of ionic liquid [BEIm]X (= 1-butyl-3-ethyl-imidazolium halide), the preparation of (bpy)MX2 (M = Pt, Pd; X = Br; bpy = 2,2′-bipyridine) was revisited using the CHCl3 solvent. The mixture of PtBr2 and [BEIm]Br in CHCl3 is in fact a CHCl3 solvent dispersed with tiny [BEIm]Br aggregates in which the PtBr2 coordination polymer dissolves. The oligomeric PtBr2 entities constantly break and reform their Pt–Br bonds all the time in the mixture when the bromide anions change from anion status to terminal/bridge ligand status, and vice versa. The kinetically grown, novel packing polymorphic (bpy)PtBr2 (1b) was obtained concurrently with (bpy)PtBr4 (2), suggesting an extrusion of polybromoplatinate step is key to the branching products 1b and 2.