SN versus S⁺N^-:  An Experimental and Theoretical Charge Density Study

Abstract

To elucidate the bonding situation in the widely discussed hypervalent sulfur nitrogen species, the charge density distributions rho(r) and related properties of four representative compounds, methyl(diimido)sulfinic acid H(NtBu)(2)SMe (1), methylene-bis(triimido)sulfonic acid H(2)C[S(NtBu)(2) (NHtBu)](2) (2), sulfurdiimide S(NtBu)(2) (3), and sulfurtriimide S(NtBu)(3) (4), were determined experimentally by high-resolution low-temperature X-ray diffraction experiments (T = 100 K). This set of molecules represents an ideal frame of reference for the comparison of SN bonding modes, because they contain short formal S=N double bonds as well as long S-N single bonds, some of them influenced by inter- or intramolecular hydrogen bonds. For comparison, the gas-phase ab initio calculations of the four model compounds, H(NMe)(2)SMe, H(2)C[S(NMe)(2)(NHMe)](2), S(NMe)(2), and S(NMe)(3), were performed. The topological features were found to be not particularly sensitive with respect to different substituents R (R = H, Me, tBu). In this paper, it is documented that theory and experiment differ in the eigenvalues of the Hessian matrix because of systematically differing positions of the bond critical points but agree very well concerning the spatial Laplacian distribution and the distinct polarization of all investigated sulfur-nitrogen bonds. Both recommend the S(+)-N(-) formulation of sulfur nitrogen bonds in 1 and 2 since all nitrogen atoms are found to be sp(3) hybridized. The planar SNx (x = 2, 3) units in the diimide 3 and the triimide 4 reveal characteristics of m-center-n-electron systems. For none of the investigated S-N bonds, a classical double bond formulation can be supported. This is further substantiated by the NBO/NRT approach. Valence expansion to more than eight electrons at the sulfur atom can definitely be excluded to explain the bonding.

Meaningful Structural Descriptors from Charge Density

“…Indeed, the S À N bonds in both compounds were found to be polar in the topological analysis of the experimentally EDD. [107] Valence shell charge concentrations (VSCCs) can be utilized to determine the density-related bonding geometry of an atom. They depict the hybridization better than do the traditional interatomic vectors.…”

A Zirconium Hydrazide as a Synthon for a Metallanitrene Equivalent: Atom‐by‐Atom Assembly of [EN2]2− Units (E=S, Se) by Chalcogen‐Atom Transfer in the Coordination Sphere of a Transition Metal

“…[21,22] The metal-ligand bonds to the two Zr centers of Zr (1) [12] This situation resembles the bonding in the organoelement analogues, the sulfur and selenium diimides, [19b] which has been established in detail both experimentally and theoretically. [23] The bonding is best described by the two resonance structures A and B.…”

Bonding Trends in Lewis Acid Adducts of S4N4 – X‐ray Structure of TeCl4·S4N4

“…This might indicate delocalization of π-electron density, but the high bond orders and consequently short S-N bond lengths have also been discussed in terms of electrostatic reinforcement of the bonds. [32][33][34][35][36] The bond orders of the M(1)-N(1) bond and the natural atomic charges of M(1) and N(1) expectedly show variation [1] [d] Ref. [2] [e] Ref.…”