Chameleonic metal-bound isocyanides: a π-donating Cu^I-center imparts nucleophilicity to the isocyanide carbon toward halogen bonding

In the structures of the isostructural cocrystals [CuI3(CNXyl)3]·CHX3 (X = Br, I), two adjacent CuI-bound isocyanide groups, whose carbon lone pairs are blocked by ligation, exhibit nucleophilic properties induced by a π-donating d10[CuI] center and function as an integrated two-center halogen bond acceptor forming bifurcated μ2-X⋯(C,C) halogen bonds. This bonding includes the electronegative regions of the two isocyanide ligands and a σ-hole of an X center of CHX3 and it is not supported by any attractive X⋯Cu interactions. The true halogen bonding nature of the μ2-X⋯(–Cu–) contacts was confirmed theoretically by DFT calculations using several computational tools (QTAIM, NCIplot, IRIPlot and IGMPlot indexes, MEP surfaces, ELF analysis, and electron density/electrostatic potential plots). Noncovalent interaction patterns of CNR ligands and also their metal-dependent chameleonic behavior toward noncovalent interactions were analyzed, considering the electronic properties of coordinating metal centers.