Classics Meet Classics: Theoretical and Experimental Studies of Halogen Bonding in Adducts of Platinum(II) 1,5-Cyclooctadiene Halide Complexes with Diiodine, Iodoform, and 1,4-Diiodotetrafluorobenzene

Abstract

Complexes of PtX2COD (X = Cl, Br, I; COD = 1,5-cyclooctadiene) were cocrystallized with classical halogen-bond donors (CHI3, I2, and 1,4-diiodotetrafluorobenzene (FIB)), resulting in noncovalently bound supramolecular aggregates of various lengths—from heterotrimers to polymers. The influence of halides in the complexes on the geometry and strength of the halogen bond (XB) was studied both experimentally by single-crystal XRD and theoretically by quantum chemical methods such as noncovalent interaction plots (NCI-plot), electrostatic potential (ESP) surface analysis, and a combination of electron localization function (ELF) and quantum theory of atoms in molecules (QTAIM) analyses. It was shown that strength of XB interactions in the adducts increases in the order CHI3 > FIB > I2. Although halogen bonding was found to be the main preorganizing force in the structures, in the case of FIB adducts a rare Pt···I interaction was involved in additional stabilization of the structure. Hence, fine-tuning of halogen bonding can influence the length of the polymer, as well as the strength and directionality of interactions in the adduct.