The solid-state structures of co-crystals of chalcogenadiazoles (ChDAs) with planar half-lantern Pt^II ₂ and mononuclear Pt^II complexes exhibit short Ch⋯Pt^II (Ch = Se, Te) contacts that occur between a metal site and the ChDA. The structures demonstrate a unique geometric feature whereby the two deep σ-holes of ChDA are turned away from a d_z²-nucleophilic Pt^II 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 σ-holes of ChDA but is involved in other types of interactions including, in particular, with a π-hole at the Ch site. The unusual linkage between a platinum(II) atom and ChDA is driven by the combined action of the Pt → π-hole on Ch bonding (30–41% of the total interaction energy) and other C⋯C/C⋯S π-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 d_z²(Pt) → π*(ChDA) charge transfer allows the assignment of the Ch⋯Pt interactions to the chalcogen bonding.

Solvent-rich dichloromethane solvate of cis-[Ir(bptz)₂(CNXyl)₂]BF₄ (3, bptz is cyclometallated 4-(4-bromophenyl)-2-methylthiazole) is prepared via the reaction of chloro-bridged dimer [Ir(bptz)₂(μ-Cl)]₂ (1) with 2,6-dimethylphenyl isocyanide (CNXyl, 2) and AgBF₄. Single crystal X-ray diffraction on the 3·3¼CH₂Cl₂ solvate showed the presence of numerous non-covalent interactions, including the C–S···F–B chalogen bonding (ChB), the C–Br···Br–C, C–Cl···Br–C, and C–Cl···S(C)–C halogen bonding (XB), and the C–H···F–B hydrogen bonding (HB). The nature of these short contacts was explored both experimentally by single-crystal X-ray diffraction and theoretically by DFT calculations on the empirical geometries followed by Bader’s topological electron density distribution analysis. The evaluated energies of XBs and ChBs are in range 1.3–2.2 kcal/mol indicating the non-covalent nature of the contacts.

Palladium(II) and platinum(II) complexes featuring metalla-N-heterocyclic carbenes (7–12) were synthesised via metal-mediated coupling between equimolar cis-[MCl₂(CNR)₂] (R = 2,6-Me₂C₆H₃ (Xyl), 2,4,6-Me₃C₆H₃ (Mes)) and 2-aminopyridine or 2-aminopyrazine. Thiocyanate complexes 13–18 with two thiocyanate ligands were obtained through the ligand exchange in the parent compounds 7–12 with NH₄CNS in acetone/CH₂Cl₂. Complexes 7–18 were isolated and characterised by HRESI⁺-MS, IR, ¹H and ¹³C{¹H} NMR spectroscopy and single-crystal X-ray diffraction (in the case of 11, 16, and 18). The UV-vis properties of 7–18 and the electrochemical properties of 7–12 were also evaluated. To study the electronic structure and bonding nature in the new compounds, the quantum theory of atoms in molecules (QTAIM) and Mayer bond order analysis together with the extended transition state with the natural orbitals for chemical valence (ETS-NOCV) method, were used. X-ray diffraction studies and theoretical considerations indicate that the thiocyanate derivatives 16 and 18 form supramolecular dimers by two symmetrical pairs M¹⋯C⁵ and S¹⋯C² with short intermolecular contacts between an electron-rich M^II-center and thiocyanate ligand on the one side and the electron-poor π-system of an azaheterocyclic ring on the other side. Representative carbenes 8, 11 and 12 were evaluated as photocatalysts for the hydrosilylation of diphenylacetylene with triethylsilane giving 1,2-(diphenylvinyl)triethylsilane in 98% yield under visible light irradiation (blue light, 445 nm).