Highly polar stacking interactions wrap inorganics in organics: lone-pair–π-hole interactions between the PdO4 core and electron-deficient arenes

Abstract

Cocrystallization of the palladium acetate cluster Pd₃(OAc)₆ (abbreviated as [Pd₃]) with electron-deficient iodine(I)-based perfluoroarenes (Ar^FI: iodopentafluorobenzene, 4-iodoheptafluorotoluene, 1,4-diiodotetrafluorobenzene, 1,2-diiodotetrafluorobenzene, and octafluoro-4,4′-diiodo-1,1-biphenyl) and iodine-free octafluoronaphthalene gave a series of six cocrystals [Pd₃]·(arene) studied by single-crystal X-ray diffractometry. Significant intermolecular noncovalent interactions were verified by a density functional theory study, molecular electrostatic potential and Hirshfeld surface analyses, a combined QTAIM/NCPlot approach, and NBO and energy framework calculations. In five out of six structures, the aromatic rings coupled with cluster [Pd₃] via lone pair–π-(Ar^F)-hole interactions. The iodine-containing arenes, Ar^FI, were additionally involved in halogen bonding with carboxylate O centers, but inorganic–organic stacking still remained the structure-determining interaction. In the stacking, the electron-rich PdO₄ plane behaved as a five-center nucleophile providing oxygen lone pairs in addition to the d_z²-Pd^II orbital; this plane complemented the π-acidic surface of the arenes, affording highly polar circular stacking, where organics wrapped inorganics.