Does a Stabilising Interaction Favouring theZ,ZConfiguration of S‐NSN‐S Systems Exist?

Abstract

The existence of the orbital interaction presented in the literature as being the cause for the stabilisation of the Z,Z configuration of Ph-S-N=S=N-S-Ph (1) and its derivatives in the crystal phase, has been investigated. The results of theoretical calculations at the DFT/B3LYP/6-311+G* level of theory suggest that such a stabilising interaction might not exist or be extremely weak and that packing forces must be the main cause of the observed Z,Z configuration in the solid. To reach this conclusion structural and energetic parameters were combined to study the bonding in these -S-N=S=N-S- systems. For the analogous Ph-Se-N=S=N-Se-Ph (2) in particular the isomeric equilibrium in solution found in the variable-temperature 77Se NMR spectrum indicates that, in the gas phase or in solution, the observed Z,Z configuration is not stabilised to a greater extent than the Z,E configuration.

Insight Into the Intermolecular Factors Responsible for theZ,ZConfiguration of Ar–X–N=S=N–X–Ar (X = S, Se) Derivatives in the Solid State

“…The bond lengths and angles in compounds 4-7 given in Table 1 are typical [11] and quite similar to those found for compounds 1-3. [3,7,8] The intramolecular X II ···X II distances are again significantly shorter than the sums of corresponding van der Waals radii, which are 3.60 Å for the S···S and 3.80 Å for the Se···Se contacts. [12,13] Despite the fact that the seven compounds display the same Z,Z configuration, their particular molecular conformations are somewhat different.…”

“…[3,7,8] This configuration features a virtually planar chalcogen-nitrogen fragment in which the X II ···X II (X = S, Se) distance is significantly shorter than the sum of the van der Waals radii. [3,7,8] According to the XRD data we present here, [9] compounds 4-7 also exist in the Z,Z configuration in the crystal; see Table 1 for geometrical data. For compound 4, the -N=S=N-fragment is disordered over two sites (see Figure 2) in a ratio of 55:45.…”

“…Recently, we have shown [3] that the Z,Z configuration of C 6 H 5 -S-N=S=N-S-C 6 H 5 (1) [7] and C 6 H 5 -Se-N=S=N-Se-C 6 H 5 (2) [3] -and consequently that of 4-ClC 6 H 4 -S-N=S=N-S-C 6 H 4 Cl-4 (3) [8] -in the crystal can not be explained by the stabilising intramolecular interaction between the X II (X = S, Se) atoms, which had been suggested in the literature, and that intermolecular forces in the crystal must be the driving force behind the observed configuration. In particular, we have demonstrated that in the gas phase or in solution the Z,Z configuration is not stabilised to a greater extent than the Z,E configuration.…”

“…[1,2] Accurately predicting and rationalising these structures, both for isolated molecules and those arranged regularly in a crystal structure, remain of obvious fundamental interest. [3][4][5] This is particularly true when it comes to identifying and understanding the correlations that exist between molecular shape and the precise nature of the packing in the crystal. Within the family of chalcogen-nitrogen compounds, the oligomeric analogues of catenated sulfur nitride, (SN) x , a metallic polymer and superconductor, [6] attract special at-lecular stereoelectronic effects.…”

“…[9] Based on the results of quantum chemical calculations (i.e. energy differences, bond orders and a topological analysis of the electron density) on 2,6-(CH 3 ) 2 C 6 H 3 -S-N=S=N-S-C 6 H 3 (CH 3 ) 2 -2,6 (4Ј) (as a model system for compound 4) and 5, using the same approach as we applied earlier, [3] intramolecular interactions can again be excluded as the reason for the observed Z,Z configurations. In order to shed more light on the possible intermolecular factors responsible for these observations, a number of simulations of the crystal packing of parent compound 1 were performed using the OPiX software.…”