Symmetry of three-center, four-electron bonds

Abstract

The factors determining the symmetry and the fundamental nature of the three-center, four-electron bonds are assessed.

Halogen Bonds of Iodonium Ions: A World Dissimilar to Silver Coordination

“…+ complex, allowing formation of a slightly destabilized yet symmetric halogen bond. As the core of 1 is more adaptable than the previously studied bidentate bis(pyridine)-type donors, 15,22 11,12,23 The former prefers an asymmetric geometry, with a distinct covalent and a distinct secondary bond, while the latter is centrosymmetric. Three-center halogen bonds have occasionally been referred to as coordinative bonds.…”

“…11, 15-20, 22, 24-27 Moreover, the three-center [N•••Ag•••N] + bond of silver(I) in the bis(pyridine) complex has been shown to be similar to the analogous Au(I) complex in solution, the solid state and in silico. 23 The analysis of statistical trends from X-ray crystallographic observations, using data obtained from the Cambridge Structural Database (CSD) indicated that the bis(pyridine) complexes of other transition metals, such as Hg(II), Cd(II), Te(III), Er(III), Zn(II), Gd(III), Mn(II), Fe(II), Ni(II), Cr(II), and Rh(I) also form linear and symmetric bis(pyridine)metal(I-III) three-center complexes with comparable geometries. 23 Accordingly, the analyses of iodine(I) and silver(I) complexes are expected to provide general conclusions to compare the bonding of halonium and transition metal complexes.…”

Hydrogen Bond and Other Lewis Acid–Lewis Base Interactions as Preliminary Stages of Chemical Reactions

“…Another challenge announced here concerns asymmetric [NXN] + systems since the symmetrical systems containing the halogen, X, are known rather from various studies [ 48 ]. For example, the experimental NMR spectroscopic and crystal structure studies as well as the theoretical calculations were performed recently on the systems containing halogen cation as well as other cations between nitrogen centres, i.e., the [NZN] + systems where Z + = H + , Li + , Na + , F + , Cl + , Br + , I + , Ag + and Au + [ 52 ]. Two series, one of bis(pyridine) entities and the second one containing the (1,2-bis(pyridin-2-ylethynyl)benzene) structure were considered [ 52 ].…”

“…For example, the experimental NMR spectroscopic and crystal structure studies as well as the theoretical calculations were performed recently on the systems containing halogen cation as well as other cations between nitrogen centres, i.e., the [NZN] + systems where Z + = H + , Li + , Na + , F + , Cl + , Br + , I + , Ag + and Au + [ 52 ]. Two series, one of bis(pyridine) entities and the second one containing the (1,2-bis(pyridin-2-ylethynyl)benzene) structure were considered [ 52 ]. In all cases the symmetrical arrangements are observed, only for Z + = H + and F + the asymmetric systems occur; this concerns both above-mentioned series.…”

“…It is worth mentioning that the potential energy curves were analysed theoretically for the bis(pyridine) series of complexes [ 52 ], the displacement of the Z + cation from the N···N mid-point was plotted versus the electronic energy of the system. The single well potential energy curve is observed for all systems except of Z + = H + , F + where the double minimum symmetrical curve occurs [ 52 ]. Since the similar situation occurs for the series of 1,2-bis(pyridin-2-ylethynyl)benzene structures thus one can expect that the potential energy curve shape depends on the cation.…”