Reverse Sandwich Structures from Interplay between Lone Pair−π-Hole Atom-Directed C···d_<i>z</i>²[M] and Halogen Bond Interactions

Abstract

4-Bromo- and 4-iodo-5-nitrophthalonitriles (BNPN and INPN, respectively) were cocrystallized with the metal acetylacetonates [M(acac)2] (M = Pd (1), Pt (2)) to give the three adducts 1·2BNPN, 2·2BNPN, and 1·2INPN, exhibiting reverse arene sandwich solid-state structures. The inspection of the XRD data for the adducts revealed new types of (lone pair)[M]···π-hole noncovalent interactions, namely atom-directed C···dz2[M] noncovalent contacts. In addition, C–X···(O,O) (X = I, Br) bifurcated halogen bonds (XBs) along with some other types of short contacts were recognized. The XRD experiments were supported by Hirshfeld surface analysis and DFT calculations: i.e., topological analysis of the electron density distribution within the framework of the QTAIM method at the ωB97XD/DZP-DKH level of theory. Estimated energies of all studied noncovalent contacts vary from 0.6 to 3.8 kcal/mol.