A new look at the chalcogen bond: pi-hole-based chalcogen (Se, Te) bonding which does not include a sigma-hole interaction

The solid-state structures of co-crystals of chalcogenadiazoles (ChDAs) with planar half-lantern PtII 2 and mononuclear PtII complexes exhibit short Ch.PtII (Ch = Se, Te) contacts that occur between a metal site and the ChDA. The structures demonstrate a unique geometric feature whereby the two deep s-holes of ChDA are turned away from a dz2-nucleophilic PtII site. A comprehensive DFT study (PBE0-D3BJ; computational tools QTAIM, ELF, IGMH, MEP, CDF, ETS-NOCV, and SAPT), focused on the analysis of these puzzling structural features, revealed that a platinum(II) center does not interact with the deep s-holes of ChDA but is involved in other types of interactions including, in particular, with a p-hole at the Ch site. The unusual linkage between a platinum(II) atom and ChDA is driven by the combined action of the Pt. p-hole on Ch bonding (30-41% of the total interaction energy) and other C.C/C.S p-hole interactions involving the ChDA and ligand's arenes. The effect of the combined action of these interactions is so expressed that the Ch.Pt interaction structurally mimics a semicoordination bond. However, significant dz2(Pt). p*(ChDA) charge transfer allows the assignment of the Ch.Pt interactions to the chalcogen bonding.