Highly polar stacking interactions wrap inorganics in organics: Lone-pair-π-hole interactions between the PdO₄core and electron-deficient arenes

Cocrystallization of the palladium acetate cluster Pd3(OAc)6 (abbreviated as [Pd3]) with electron-deficient iodine(i)-based perfluoroarenes (ArFI: 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-(ArF)-hole interactions. The iodine-containing arenes, ArFI, 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 dz2-PdII orbital; this plane complemented the π-acidic surface of the arenes, affording highly polar circular stacking, where organics wrapped inorganics.