Different Stacking Types in a Single Hybrid Cocrystal System: π···π- and π-Hole-Based Organic-Inorganic Planar Assemblies.

The planar bis-chelated complex [Pd(NO)] (; NO = 4-MeCHNNC(O)NMe) exhibits two distinct stacking modes with electron-deficient aromatics: π···π stacking with hexafluorobenzene (CF) versus charge-transfer π-hole interactions with 1,2,4,5-tetracyanobenzene (TCB). Cocrystallization of the complex with CF or TCB yields cocrystals ·3(CF) and ·2TCB, respectively, which display different colors and stacking patterns despite similar structural motifs. Comprehensive analysis using X-ray diffraction, combined with quantum theory of atoms-in-molecules (QTAIM), an independent gradient model based on Hirshfeld partition (IGMH), extended transition state natural orbital for chemical valence theory with charge displacement function (ETS-NOCV/CDF), many-body interaction analysis, and symmetry-adapted perturbation theory (SAPT), reveals fundamentally different interaction mechanisms. In 3(CF), the stacking is primarily governed by intermolecular polarization without significant charge transfer, with dispersion forces contributing approximately 70% of the attractive energy. In contrast, ·2TCB exhibits pronounced charge transfer (35 me) and significant inductive components alongside dispersion forces, characteristic of π-hole interactions. This dichotomy in stacking behavior provides new insights into the nature of organic-inorganic planar assemblies and demonstrates that seemingly similar structural patterns can arise from distinctly different combinations of noncovalent forces, which is essential for rational crystal engineering of hybrid materials.