The Electronic Structure and Localized Molecular Orbitals in S₄N₄ by the CNDO/BW Theory

Abstract

The energies calculated for tetranitrogen tetrasulfide, S4N4, by the CNDO/BW theory favor a structure with coplanar nitrogen atoms and not a structure with coplanar sulfur atoms. Both structures have been proposed from experimental studies. Localized molecular orbitals are calculated for S4N4 and used to choose the appropriate Lewis structure for the molecule. The hybridization at the nitrogen and sulfur atoms is discussed. There is electron delocalization in the molecule, the S—N bond is a bent bond involving pure p-orbitals on the sulfur and nitrogen atoms and there is a pure p-bent bond between the sulfur atoms on the same side of the coplanar nitrogen atoms. There is no N—N bond in S4N4.

Localized molecular orbitals for dinitrogen dioxide, dinitrogen trioxide, and dinitrogen tetroxide

“…The N2 orbitals are sp2•55 hybridized; the N ¡ orbital is pure px. In the CNDO/2 LMO picture the 03 "lone pair" III has d = 23.3% (0.46 e) compared to CNDO/BW with d = 18.6% (0.37 e), while the 02 lone pair II has d = 26.0% (0.52 e) instead of 21.1% (0.42 e). The N-N bond d = 1.54% (0.03 e) instead of 3.96% (0.08 e).…”

Analysis of the Explosive Properties of Tetrasulfur Tetranitride, S4N4

“…The long S⋅⋅⋅S bond has also been the studied recently at high level of theory and found to be determined mainly due to strong and complex electron correlation effects [35] . Calculations at different levels of sophistication [36,42] show that both S−N and S−S bond paths are bent in‐ and outwards typical for a strained molecule explaining its high energy content in comparison to other homoleptic S−N species [37] …”

“…The overall bonding in S 4 N 4 can be rationalized assuming formal positive and negative charges at both sulfur, and nitrogen respectively [36–38] (Figure 2).…”

Vibrational Spectra and Force Constants of Tetrasulfurtetranitride, S4N4 [1]

“…This indicates that the SN bond order in S 4 N 4 cannot be much higher than in S 4 (NH)4 despite the somewhat smaller bond distance (S 4 N 4 : 162, S 4 (NH) 4 : 167 pm). Using the relationship / r (SN) = 145 dgjj-00 (<2 in A) derived from the data of only seven SN compounds [36] one obtaines / r = 5.0 N-cm -1 for S 4 N 4 and 4.1 N-cm -1 for S 4 (NH) 4 indicating that this equation cannot be applied to S 4 N 4 .That the shorter SN bonds in S 4 N 4 than in (SNH)4 do not indicate any appreciable double bond character has also been concluded from molecular orbital calculations[6,7] and is in agreement with measurements of the 14 N [37] and 15 N [15] chemical shifts which correspond better with the values found for nitrogen in SN single bonds than in SN double bonds. If one prefers a valence bond picture, the following structure seems to represent the bonding situation best:…”