Structures and EPR spectra of binary sulfur–nitrogen radicals from DFT calculations

Abstract

The scattered electron paramagnetic resonance (EPR) spectroscopic data for binary sulfurnitrogen (S,N) radicals has been compiled and critically assessed. Many of these are inorganic rings or cages. For each species, possible equilibrium structures in the gas phase and the EPR hyperfine coupling (hfc) constants have been calculated with DFT using the B3LYP functional and basis sets of triple- (or better) quality. Good agreement is obtained (through isotopic enrichment). These values were essential for the correct identification of the EPR spectra of this important radical which previously was missassigned to other species.Our results suggest that 33 S data will be equally important for the correct identification of the EPR spectra of other binary S,N species, many of which are cyclic systems, e.g.

Electrochemical and Electronic Structure Investigations of the [S3N3]•Radical and Kinetic Modeling of the [S4N4]n/[S3N3]n(n= 0, −1) Interconversion

“…The electronic structure of [S3N3] • has most recently been examined by us using density functional theory (DFT). 14 The calculations fully supported a planar ring geometry with a 2 A2 ground state, in excellent agreement with the previous HartreeFock and CI calculations employing basis sets of minimal and double-zeta quality. 15 The radical has C2v symmetry but the geometrical distortions are very small when the optimized structure is contrasted with that of the diamagnetic D3h symmetric [S3N3]  anion.…”

“…In connection with our interest in the characterization of short-lived, binary S,N radicals, 14 we now report the application of these methods to detailed investigations of (a) the reduction of S4N4 and (b) the oxidation of [S3N3] -. In part (a) we have used the SEEPR technique to acquire high quality EPR spectra of the anion radical [S4N4] -• using natural abundance, 15 N and 33 S-enriched S4N4 at low temperature.…”

The Synthesis and Characterization of Stable Radicals Containing the Thiazyl (SN) Fragment and Their Use as Building Blocks for Advanced Functional Materials

“…This radical is one of the main gas phase species (detected using photoelectron spectroscopy) from the vaporization of poly(thiazyl), (SN) x (see below) or from the pyrolysis of the cage molecule S 4 N 4 (2). 21,22 The prediction of a planar, cyclic structure for 1 was supported by calculations using varying levels of theory (ab initio HF, 22 DFT 14 and multiconfigurational 23 studies), although the ring structure is predicted to be slightly distorted from the ideal D 3h structure; the incomplete occupancy of the upper degenerate π molecular orbitals is predicted to lead to a Jahn-Teller distortion to a C 2v symmetry structure (Figure 9.2). The corresponding closed shell anion S 3 N 3 − is a stable species whose structure and reaction chemistry have been explored, 24,25 but the seemingly facile entry into the neutral radical via one-electron oxidation of S 3 N 3 − -either chemically or electrochemically -has failed to lead to detectable quantities of the neutral radical in solution.…”

“…Boeré and Chivers have compiled calculated and (where available) EPR spectroscopic characterization of a wide range of binary SN compounds, both neutral and charged. 14 …”

“…The corresponding closed shell anion S 3 N 3 − is a stable species whose structure and reaction chemistry have been explored, 24,25 but the seemingly facile entry into the neutral radical via one-electron oxidation of S 3 N 3 − -either chemically or electrochemically -has failed to lead to detectable quantities of the neutral radical in solution. 14,15,25,23 …”