Structure-directing sulfur...metal noncovalent semicoordination bonding

The abundance and geometric features of nonbonding contacts between metal centers and `soft' sulfur atoms bound to a non-metal substituentRwere analyzed by processing data from the Cambridge Structural Database. The angular arrangement ofM, S andRatoms with ∠(R—S...M) down to 150° was a common feature of the late transition metal complexes exhibiting shortenedR—S...Mcontacts. Several model nickel(II), palladium(II), platinum(II) and gold(I) complexes were chosen for a theoretical analysis ofR—S...Minteractions using the DFT method applied to (equilibrium) isolated systems. A combination of the real-space approaches, such as Quantum Theory of Atoms in Molecules (QTAIM), noncovalent interaction index (NCI), electron localization function (ELF) and Interacting Quantum Atoms (IQA), and orbital (Natural Bond Orbitals, NBO) methods was used to provide insights into the nature and energetics ofR—S...Minteractions with respect to the metal atom identity and its coordination environment. The explored features of theR—S...Minteractions support the trends observed by inspecting the CSD statistics, and indicate a predominant contribution of semicoordination bonds between nucleophilic sites of the sulfur atom and electrophilic sites of the metal. A contribution of chalcogen bonding (that is formally opposite to semicoordination) was also recognized, although it was significantly smaller in magnitude. The analysis ofR—S...Minteraction strengths was performed and the structure-directing role of the intramolecularR—S...Minteractions in stabilizing certain conformations of metal complexes was revealed.