Theoretical confirmation of existence of X⋯Au non-covalent contacts

Wolfium bonds in homodimers of MX4Y (M = Mo, W; X = F, Cl, Br; Y = O, S, Se)

The term "wolfium bond" has been recently introduced to describe the noncovalent attraction between an atom of group 6 and a nucleophile via a σ-hole binding site. Crystal structures commonly contain a motif wherein two MX4Y units are arranged in close proximity, where M represents either Mo or W, and X and Y refer to halogen and chalcogen atoms respectively. DFT calculations were thus applied to a wide range of homodimers of these molecules so as to assess their preferred arrangements, and to characterize the types of bonding that are present in each in a systematic manner. The most stable Dual-X configuration is symmetric and contains a pair of equivalent M⋯X bonds. The interaction energies range from -8 to -29 kcal mol-1, and are largest for X = F, Y = O, and M = W. The X electron donor is replaced by Y, and the two wolfium bonds are reduced to one, in the less stable Mono-Y structure, with interaction energies between -2 and -10 kcal mol-1. There is some question as to whether the weaker bonds of this type constitute true wolfium bonds.

Exploring Au(i) involving halogen bonding with N-heterocyclic carbene Au(i) aryl complexes in crystalline media

Among the known types of non-covalent interactions with a Au(i) metal center, Au(i) involving halogen bonding (XB) remains a rare phenomenon that has not been studied systematically. Herein, using five N-heterocyclic carbene (NHC) Au(i) aryl complexes and two iodoperfluoroarenes as XB donors, we demonstrated that the XB involving the Au(i) metal center can be predictably obtained for neutral Au(i) complexes using the example of nine co-crystals. The presence of XB involving the Au(i) center was experimentally investigated by single-crystal X-ray diffraction and solid-state ¹³C CP-MAS NMR methods, and their nature was elucidated through DFT calculations, followed by electron density, electrostatic potential, and orbital analyses. The obtained results revealed a connection between the structure and HOMO localization of Au(i) complexes as XB acceptors, and the geometrical, electronic, and spectroscopic features of XB interactions, as well as the supramolecular structure of the co-crystals.

On the nature of recurrent Au⋯π motifs in tris(2,2'-bipyridine)M(II) (M = Fe, Co and Ni) dicyanoaurate(I) salts: X-ray analysis and theoretical rationalization

This manuscript reports the synthesis, X-ray characterization and DFT study of three new [M(bipy)₃]₂[Au(CN)₂]₃(X) (M = Fe, Co, and Ni; bipy = 2,2'-bipyridine; X = anion) ionic compounds. These salts are composed of [M(bipy)₃]²⁺ dications and [Au(CN)₂]^- anions in a 2 : 3 ratio. The positive charge is compensated by X = Cl^- anions in compounds 1 (M = Fe) and 2 (M = Co) and X = OH^- in 3 (M = Ni). The three tridentate bipyridine ligands define the coordination of the M²⁺ cation, resulting in a nearly octahedral coordination sphere. The linear dicyanoaurate(I) anions are completely surrounded by a cradle of aromatic rings with Au-ring centroid distances below the sum of van der Waals radii, evidencing the existence of a specific Au⋯π attraction. This interaction has been analyzed in terms of the role of the Au-atom (Lewis acid or Lewis base) using DFT calculations combined with the quantum theory of atoms in molecules (QTAIM), noncovalent interaction plot index (NCIplot) and natural bond orbital (NBO) computational tools. The NBO suggests that the Au⋯π interaction is an example of a coinage bond in spite of the anionic nature of the acceptor and the cationic nature of the donor.

Metal Centers as Nucleophiles: Oxymoron of Halogen Bond-Involving Crystal Engineering

This review highlights recent studies discovering unconventional halogen bonding (HaB) that involves positively charged metal centers. These centers provide their filled d‐orbitals for HaB, and thus behave as nucleophilic components toward the noncovalent interaction. This role of some electron‐rich transition metal centers can be considered an oxymoron in the sense that the metal is, in most cases, formally cationic; consequently, its electron donor function is unexpected. The importance of Ha⋅⋅⋅d‐[M] (Ha=halogen; M is Group 9 (Rh, Ir), 10 (Ni, Pd, Pt), or 11 (Cu, Au)) interactions in crystal engineering is emphasized by showing remarkable examples (reported and uncovered by our processing of the Cambridge Structural Database), where this Ha⋅⋅⋅d‐[M] directional interaction guides the formation of solid supramolecular assemblies of different dimensionalities.

Unprecedented [d9]Cu[d10]Au coinage bonding interactions in {Cu(NH3)4[Au(CN)2]}+[Au(CN)2]- salt

The X-ray structure of the {Cu(NH₃)₄[Au(CN)₂]}⁺[Au(CN)₂]^- salt is reported showing an unprecedented [d⁹]Cu[d¹⁰]Au coinage bond. The physical nature of the interaction has been studied using DFT calculations, including the quantum theory of atoms-in-molecules, the noncovalent interaction plot and the natural bond orbital analysis, revealing the nucleophilic role of the [d¹⁰]Au metal and the electrophilic role of [d⁹]Cu metal.

Extended Assemblies of Ru(bpy)(CO)2X2 (X = Cl, Br, I) Molecules Linked by 1,4-Diiodotetrafluoro-Benzene (DITFB) Halogen Bond Donors

The ruthenium carbonyl compounds, Ru(bpy)(CO)2X2 (X = Cl, Br or I) act as neutral halogen bond (XB) acceptors when co-crystallized with 1,4-diiodotetrafluoro-benzene (DITFB). The halogen bonding strength of the Ru-X⋅⋅⋅I halogen bonds follow the nucleophilic character of the halido ligand. The strongest halogen bond occurs between the chlorido ligand and the iodide atoms of the DITFB. All three halogen bonded complexes form polymeric assemblies in the solid state. In Ru(bpy)(CO)2Cl2⋅DITFB (1) and in Ru(bpy)(CO)2Br2⋅DITFB (2) both halido ligands are halogen bonded to only one DITFB donor. In Ru(bpy)(CO)2I2⋅DITFB (3) only one of the halido ligands is involved in halogen bonding acting as ditopic center for two DITFB donors. The polymeric structures of 1 and 2 are isomorphic wave-like single chain systems, while the iodine complexes form pairs of linear chains attached together with weak F⋅⋅⋅O≡C interactions between the closest neighbors. The stronger polarization of the iodide ligand compared to the Cl or Br ligands favors nearly linear C-I⋅⋅⋅I angles between the XB donor and the metal complex supporting the linear arrangement of the halogen bonded chain.

Halogen bonding-assisted assembly of bromoantimonate(v) and polybromide-bromoantimonate-based frameworks

Halogen bonding within bromo- and polybromoantimonates(v).