Conformations and Energetics of Sulfur and Selenium Diimides

Abstract

The geometries and energetics of different conformations of sulfur and selenium diimides E(NR)2 (E = S, Se; R = H, Me, t Bu, C6H3Me2-2,6, SiMe3) have been studied by using various ab initio and DFT molecular orbital techniques. The syn,syn conformation is found to be most stable for parent E(NH)2 but in general the preferred molecular conformation for substituted chalcogen diimides is syn,anti. In the case of E(NH)2 the present calculations further confirm that syn,syn

Formation, Structural Characterization, and Calculated NMR Chemical Shifts of Selenium‐Nitrogen Compounds from SeCl4 and ArNHLi (Ar = supermesityl, mesityl)

“…It has been well-established by recent MO calculations that for a majority of sulfur and selenium diimides the syn,anti and syn,syn conformations lie lower in energy than the anti,anti conformations [13,18]. In case of 1, however, the anti,anti conformation is found to be energetically most favourable at PBE0/TZVP level of theory, though the syn, anti and syn,syn conformations lie only 11 and 10 kJ mol Ϫ1 higher in energy, respectively.…”

“…tert-Butyl selenium di-imide also forms an N,NЈ-chelated adduct with SnCl 2 [11] and has been used to generate the dianion Se(N t Bu) 3 2Ϫ that is isoelectronic with SeO 3 2Ϫ [12]. It has been shown by X-ray crystallography in the solid state and by electron diffraction in the gas phase that different sulfur diimides exhibit either syn,anti or syn,syn conformations depending on the organic substituent [13]. The structural information for selenium diimides is much sparser.…”

“…It is well-established that sulfur diimides exclusively exist as monomeric species [13]. By contrast, tert-butyl tellurium diimide is dimeric both in solution and in solid state [15Ϫ17].…”

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

“…[5,6] These materials have possible applications as molecular wires in the field of molecular electronics. [2,7,8] It is known that the molecular geometry of catenated sulfur-nitrogen compounds, based on the three possible orientations of the substituents at each N=S=N fragment-Z,E, Z,Z and E,E, of which the Z,E configuration usually is the most stable [9,10] -depends on the stereoelectronic demand of the a,w-substituents in an unpredictable way. In many cases severely nonplanar molecular conformations were observed [11,12] which are in effect useless for molecular electronics due to the broken p-conjugation.…”

CH3N=SF2=NCH3: Structural, Conformational, and Configurational Properties in the Gaseous and in the Condensed Phases

“…For sulfur diimides that possess bulkier substituents, the anti – syn conformation was found to be the most stable form. However, rather different equilibrium patterns were observed by gas electron diffraction for CH 3 –N=S=N–CH 3 17,18 and CF 3 –N=S=N–CF 3 :11 whereas an anti – anti structure was observed for the methyl derivative, an anti – syn / syn – syn mixture was found for its fluorinated counterpart. Since the conformational properties of these compounds cannot be explained in terms of steric interactions, the conformational properties were rationalized on the basis of orbital interactions of sulfur and nitrogen lone pairs [lp(S) and lp(N)] with vicinal σ* orbitals 19.…”