Competition between coordinated halides and platinum(II) centers as halogen bond acceptors: a structural and computational study

This study investigates the supramolecular assembly and site-selectivity of halogen bonding in a series of square-planar platinum(II) complexes. Using 1,4-diiodotetrafluorobenzene (FIB) as a halogen bond donor, five cocrystals were synthesized and structurally characterized to probe the competition between coordinated halide ligands (Cl, Br, I) and the platinum(II) metal center as potential halogen-bond acceptors. X-ray structural analysis reveals that, for the chloride and bromide complexes, the supramolecular assembly is governed by highly directional I···Cl and I···Br halogen bonds. In contrast, a distinct structural transition occurs in the iodide complex, where the platinum(II) center outcompetes the coordinated halide and becomes the primary electron donor, giving rise to I···Pt halogen bonds. These experimental observations are supported by comprehensive theoretical calculations: Molecular Electrostatic Potential (MEP) surfaces, together with QTAIM and NCIplot analyses, confirm the presence of these structure-directing halogen-bonding interactions, while Natural Bond Orbital (NBO) analysis quantifies the associated charge-transfer effects and confirms the active participation of the platinum d z 2 orbital in the I···Pt contacts. Taken together, these results demonstrate that the halogen-bonding behavior of Pt(II) complexes can be tuned through the nature of the coordination environment, offering new insight into the design of metal-containing supramolecular architectures.