Halogen Bonding Involving Palladium(II) as an XB Acceptor

The half-lantern Pd-2(II) complexes trans-(O,C)-[Pd(ppz)(mu-(ON)-N-boolean AND)]2 (1) and trans-(E,N)-[Pd(ppz)(mu-(EN)-N-boolean AND)] 2 ((EN)-N-boolean AND is a deprotonated 2-substituted pyridine; E = S (2), Se ( 3); Hppz = 1-phenylpyrazole) were cocrystallized with 1,4-diiodotetrafluorobenzene (FIB) to give cocrystals 1 center dot(FIB) and (2-3)center dot 2(FIB); the parent complexes and the cocrystals were studied by X-ray crystallography. The crystal structure of trans-(O,C)-1 center dot FIB is assembled mainly by the I center dot center dot center dot O halogen bonding (XB) to give the [@Pd-2(II)]O center dot center dot center dot I(arene(F))I center dot center dot center dot O[@Pd-2(II)] linkage, while trans-(E, N)-( 2-3)center dot 2(FIB) are built by the joint action of I center dot center dot center dot Pd and I center dot center dot center dot E XBs, thus furnishing the Pd-2(II)center dot center dot center dot I(arene(F))I center dot center dot center dot E[@Pd-2(II)] (E = S, Se) cluster. Detailed theoretical (DFT) studies with the application of the QTAIM, ELF, NBO, IGM, SAPT, and HSAB methods revealed several types of attractive noncovalent interactions in the cocrystals, namely, the I center dot center dot center dot Pd, I center dot center dot center dot E (E = O, S, Se), I center dot center dot center dot C, pi-pi-stacking, and pi center dot center dot center dot F interactions. I center dot center dot center dot Pd is a rare type of XB involving the metal center as an XB acceptor, the Pd center dot center dot center dot Pd communication facilitating the I center dot center dot center dot Pd bonding. The I center dot center dot center dot Pd and I center dot center dot center dot E bonds are comparable in strength (the bond interaction energies being between -7 and -13 kcal/mol), but the former is controlled by dispersion forces, while the latter is mostly governed by an electrostatic term.

Automated summary

This study investigated the crystal structures of Pd-2(II) half-lantern complexes and cocrystals through X-ray crystallography, revealing the significant roles played by various noncovalent interactions such as I···Pd and I···E.