Metal-Involving Halogen Bonding Including Gold(I) as a Nucleophilic Partner. The Case of Isomorphic Dichloroaurate(I)·Halomethane Cocrystals.

Three isomorphic cocrystals were obtained via the crystallization of [PPN][AuCl 2 ] ( 1 ) from CHBr 3 ( 1 ·CHBr 3 ), or CHCl 3 /1,2-C 2 F 4 Br 2 ( 1 ·CHCl 3 ) and CH 2 Cl 2 /Et 2 O ( 1 ·CH 2 Cl 2 ) mixtures. Analysis of the single-crystal X-ray diffraction data for these cocrystals revealed a gold(I)-involving two-center C-X···Au halogen bond (abbreviated as XB; X = Cl, Br) and a three-center bifurcated C-Br···( Cl - Au ) XB; in the latter, the gold(I)-chloride linkage functions as an integrated XB acceptor. The noncovalent nature and energies [spanning from -1.58 to -5.52 kcal/mol for C-X···Au and -6.37 kcal/mol for C-Br···( Cl - Au ) XBs] of these noncovalent interactions were studied by density functional theory calculations and topological analysis of the electron density distribution in the framework of the quantum theory of atoms-in-molecules (QTAIM) followed by noncovalent interaction (NCI) analysis at the B3LYP-D3/jorge-TZP-DKH level of theory. The nucleophilicity of the gold(I) centers toward halogens of halomethanes was verified by a set of independent methods including electrostatic potential surfaces, electron localization function projection, natural bond orbital charge transfer, electron density/electrostatic potential profile, Wiberg bond indexes, natural population analysis, and atoms-in-molecules charge analyses.