Edward G. Awere

The high yield preparation, characterisation, and gas phase structure of the thermally stable CF3CSNSCCF3·, 4,5-bis(trifluoromethyl)-1,3,2-dithiazolyl and the X-ray crystal structure of benzo-1,3,2-dithiazolyl

The very thermally stable, but photochemically sensitive radical, 4,5-bis(trifluoromethyl)-1,3,2-dithiazolyl has been prepared, isolated, and fully characterised including a gas phase structure, and found to be paramagnetic in the liquid state at room temperature; the X-ray structure of benzo-1,3,2-dithiazolyl has been obtained for comparison.

The preparation, characterization in solution of the 7π radical 1,2,4-triseleno-3,5-diazolylium and the 6π(1,2,4-triseleno-3,5-diazolium)2+ cations, and the X-ray crystal structures of (SeNSeNSe)2(AsF6)2 and SeNSeNSe(AsF6)2 containing the first stable binary selenium–nitrogen species

([graphic omitted])n(AsF6)2(n= 1,2) containing the first stable binary selenium–nitrogen species, have been prepared by the reaction of stoicheiometric quantities of Se4(AsF6)2(n= 2) or AsF5(n= 1 and 2) with Se4N4 in liquid SO2, and their structures determined by X-ray crystallography; in solution ([graphic omitted]e)2(AsF6)2 gives the indefinitely stable 7π radical [graphic omitted]e+˙(e.s.r. spectrum of frozen powder), and [graphic omitted](AsF6)2 the 6π [graphic omitted]e2+(Raman and 14N n.m.r. spectra).

The standard molar enthalpy of formation at 298.15 K of S2N+AsF6− by fluorine combustion calorimetry

The energy of combustion of S2N+AsF6− in high-pressure fluorine has been measured calorimetrically. The only fluorine-containing gases formed in the combustion were SF6 and AsF5; both NF3 and AsF3 were sought, but not detected. The standard molar enthalpy change for the reaction: S2N+AsF6−(cr) + (112)F2(g) = 2SF6(g) + (12)N2(g) + AsF5(g), was −(2265.6±1.5) kJ·mol−1. From this value was calculated the standard molar enthalpy of formation: ΔfHmo(S2N+AsF6−, cr, 298.15 K) = −(1413.8±1.9) kJ·mol−1 at po = 101.325 kPa.

Preparation and characterisation of thermally stable (SeNSeNSe)n(AsF6)2 containing the ‘electron-rich aromatic’ 6π(SeNSeNSe)2+(n= 1) and 7π SeNSeNSe˙+(n= 2)

Crystalline thermally stable ([graphic omitted]e)n(AsF6)2 containing the ‘electron-rich aromatic’ 6π [graphic omitted]e2+(n= 1) and 7π radical cation [graphic omitted]e˙+(n= 2) were prepared in high yields from reactions of Se4N4 with stoichiometric quantities of Se4(AsF6)2(n= 1) or AsF5(n= 1 or 2) in liquid SO2 and their X-ray crystal structures determined. The structure of [graphic omitted]e(AsF6)2 consists of discrete planar [graphic omitted]e2+ cations and AsF6– anions, and that of ([graphic omitted]e)2(AsF6)2 consists of two identical, but crystallographically different, discrete ([graphic omitted]e˙+)2 cations and AsF6– anions. The centrosymmetric ([graphic omitted]e˙+)2dimer contains two planar [graphic omitted]e˙+ radical cations weakly joined by two long Se ⋯ Se bonds [2 × 3.123(3), 2 × 3.149(3)A]. There are significant cation–anion interactions in both salts. The Se–Se [2.334(3)A] and Se–N bond lengths [average: 1.74(3)(side), 1.69(3)A(top)] in [graphic omitted]e2+ are shorter than their corresponding distances in the 7π [graphic omitted]e˙+[average: Se–Se 2.398(3); Se–N 1.76(2)(side), 1.69(2)(top)A] consistent with removal of the unpaired electron from the π* singly occupied molecular orbital of the monocation. Surprisingly only one peak, rather than the expected two, was observed in the 77Se NMR spectrum of [graphic omitted]e(AsF6)2 consistent with fluxional behaviour in solution. The 77Se chemical shift [–70 °C, δ(Me2Se)= 2434, ν½= 10 Hz] is the highest so far recorded and is consistent with the dipositive charge and ‘electron-rich’ 6π aromatic character. The 77Se and 14N NMR [room temperature (r.t.), δ(MeNO2)=–67.6, ν½= 200 Hz] and the Raman spectrum in liquid AsF3 at 10 °C are all consistent with retention of the [graphic omitted]e2+ ring structure in solution. The ESR spectrum of [graphic omitted]e˙+ in SO2 solution at r.t. (g= 2.043, broad) and the spectrum of powdered [graphic omitted]e˙+ in frozen SO2 at –160 °C were similar to but not identical with those of [graphic omitted]e˙+, [graphic omitted]˙+ and [graphic omitted]˙+ indicative of a planar 7π ring system.

The preparation and characterisation by Raman spectroscopy of AsBr4+AsF6– containing the tetrabromoarsenic(V) cation

The thermodynamically unstable AsBr4+AsF6– was prepared by the reaction of AsBr3, Br2, and AsF5 at low temperatures, and characterised by Raman Spectroscopy.

Preparation and characterisation of (SeNSNS)n(AsF6)2 containing the ‘electron-rich aromatic’ 6π SeNSNS2+(n= 1) and 7π SeNSNS˙+(n= 2)

Attempted syntheses of SeNSAsF6 from the reactions of SNAsF6 with Se8(AsF6)2(4 : 1) or Se (1 : 1) gave ([graphic omitted])n(AsF6)2(n= 1 and 2), Se4(AsF6)2 and trace amounts of [graphic omitted]e(AsF6)2 and (Se/[graphic omitted]e)2(AsF6)2. The formation of ([graphic omitted])n(AsF6)2(n= 1 and 2) as the major product is consistent with generation of a SeNS+ intermediate which undergoes a concerted symmetry-allowed cycloaddition reaction with SN+ to give [graphic omitted]2+. The crystal structure of [graphic omitted](AsF6)2 consists of disordered [graphic omitted]2+ cations and AsF6– anions, that of ([graphic omitted])2(AsF6)2 consists of AsF6– anions and two independent disordered [graphic omitted]˙+ radical cations weakly linked into a non-centrosymmetric dimer by two long Se ⋯ S bonds [3.12(4), 3.09(2); 3.32(5), 3.16(6)A]. The structure of (Se/[graphic omitted]e)2(AsF6)2 contains a 50:50 mixture of disordered [graphic omitted]e˙+ and [graphic omitted]˙+ radical cations joined by two long Se/S ⋯ Se bonds [3.077(3), 3.138(3)A]. There are significant interionic interactions in all the salts. The 77Se [–60 °C, δ(Me2Se)= 2422.4, ν½, = 10.4 Hz] and 14N NMR [room temperature (r.t.), δ(MeNO2)= 68.9, ν½, = 446 Hz] spectra of [graphic omitted]2+ are consistent with a delocalised 6π ring structure. The [graphic omitted]2+ cation readily reacts with CCl3F to give Cl[graphic omitted]AsF6 the identity of which was confirmed by the determination of its crystal structure. The ESR spectrum of [graphic omitted]˙+ in SO2 solution at r.t. (g= 2.026, broad) and the spectrum of powdered [graphic omitted]˙+ in frozen SO2 at –160 °C were similar to but not identical with those of [graphic omitted]e˙+, [graphic omitted]e˙+ and [graphic omitted]˙+ indicative of a planar 7π system.

Preparation of SeNSNSe(AsF6)2 and structural characterisation of the 6π‘electron-rich aromatic’ SeNSNSe2+

Highly crystalline [graphic omitted]e(AsF6)2 was prepared by the oxidation of ([graphic omitted]e)2(AsF6)2 with AsF5 in liquid SO2. The X-ray crystal structure was determined which consists of discrete planar [graphic omitted]e2+ cations and AsF6– anions with significant cation–anion interactions. The average Se–N [1.70(2)], S–N [1.59(1)] and Se–Se [2.310(2)A] bond distances are consistent with the removal of the unpaired electron from the π* singly occupied molecular orbital of the 7π [graphic omitted]e˙+. The 77Se [–70 °C, δ(Me2Se)= 2411.7, v½= 10.2 Hz] and 14N NMR [r.t., δ(MeNO2)=–72.5, v½= 690 Hz] and Raman spectrum in AsF3 solution are all consistent with retention of the ring structure in solution. The reaction of Se4(AsF6)2 and S4N4 was reinvestigated and found to give appreciable amounts of ([graphic omitted])2(AsF6)2 and ([graphic omitted])2(AsF6)2 as well as the reported ([graphic omitted]e)2(AsF6)2. A pure sample of ([graphic omitted]e)2(AsF6)2 was prepared by reduction of [graphic omitted]e(AsF6)2 with CsN3.

The preparation, characterization in solution of the 7 π radical 1,2,4-triseleno-3, 5-diazolylium, and the 6π 1,2,4-triseleno-3-5-diazolium (2+) cations, and the X-ray crystal structures of (SeNSeNSe)2(AsF6)2 and SeNSeNSe(AsF6)2 containing the first stable binary selenium-nitrogen species

Abstract Numerous binary sulphur-nitrogen species have been prepared and structurally characterized. Analogous Selenium-nitrogen compounds are restricted to Se4N4 which is even more thermodynamically and kinetically unstable than S4N4. As a result for a search for SeNSe+ [cf. SNS+, which has a very extensive chemistry [1]] we prepared ( SeNSeNS e)2(AsF6)2 and SeNSeNS e(AsF6)2 by a variety of routes, containing the first reported thermally stable binary selenium nitrogen species including the indefinitely stable 7π radical cation SeNSeNS e+.. These salts were fully characterized both in the solid state [X-ray], and in solution, [ SeNSeNS e+., e.s.r.; SeNSeNS e2+, Raman, 14N, 77Se N.M.R.]. Interestingly SeNSeNS e2+ retains its ring structure in solution in contrast to SNSNS 2+, in solid S3N2(AsF6)2, which dissociates to NS+ and SNS+ [2].

Energetics and reaction pathways of some reactions leading to SNSAsF6 and SNAsF6

Our previously reported preparation of SNSAsF6 from S4N4, S8 and AsF5 was investigated in situ by 14N NMR spectroscopy with, and without, traces of Br2. Reaction pathways are proposed, which were separately investigated by 14N NMR spectroscopy, and an efficient high-yield synthesis of highly crystalline SNSAsF6 developed. The enthalpy of reaction was estimated as –104.6 ± 2 kJ mol–1 per SNSAsF6. The compound SNSAsF6 was also formed rapidly and quantitatively from SNAsF6 and S8 with no observable intermediates (A reaction mechanism is proposed and the enthalpy and entropy of the reaction estimated as –66 ± 28 kJ mol–1 and –1.6 J K–1 mol–1), from reactions of S4(AsF6)2 with (S3N2)2(AsF6)2(1 : 1) and S4N4(2 : 1), and very slowly in small amounts from S4N4(AsF6)2 with S8, S8(AsF6)2 or S4(AsF6)2. The compounds S4(AsF6)2 and S4N4 gave (S3N2)2(AsF6)2 and an IR spectrum of the pure material is reported. The compounds (S3N2)2(AsF6)2 was oxidised by AsF5 to give equimolar amounts of SNAsF6 and SNSAsF6 in SO2 solution, the reaction proceeding faster with traces of Br2. The enthalpy of reaction of S4N4 and AsF5 leading to SNAsF6 was estimated as –40 ± 28 kJ mol–1 per SNAsF6 and subsequently the reaction was shown to occur in about 30% yield. As part of an investigation into the course of this reaction, polymeric (S5N5AsF6)x was prepared in high yield, from S4N4 and S4N4(AsF6)2, which on oxidation with AsF5 and traces of Br2 gave SNAsF6 in a 30% yield. In addition, (S3N2)2NAsF6 was oxidised by AsF5 with traces of Br2 to give SNSAsF6, SNAsF6 and N2.

The kinetics and thermodynamics of some halogen facilitated oxidation reactions of AsF5; and the preparation and energetics of formation and x-ray Crystal structure of S3N2(AsF6)2 containing the lattice stabalized S3N22+

Abstract An excess of AsF5 oxidises sulphur only as far as S8(ASF6)2 even under forcing conditions, whereas in the presence of a trace of halogen X2(XBrClI) crystalline S4(AsF6)2 is quantitatively formed according to eq. (1) in SO2 within minutes The thermodyamics and kinetics of this reaction and related reactions leading to SNSAsF6 and SNAsF6 will be presented (S3N2)2(AsF6)2 is quantitatively oxidised by AsF5 in the presence of traces of bromine to give SNAsF6 and SNSAsF6 in SO2. Single crystals of S3N2(AsF6)2 are obtained at O°C effecting the concerted symmetry allowed cycloaddition of SN+ and SNS+. The crystal structure of S3N2(AsF6)2 is isomorphous with all SexS3−xN2(AsF6)2 (x = 1,2,3) salts, and contains planar SNSNS 2+ rings with a geometry very similar to that calculated. Although it is a 6π system and often cited in sulphur-nitrogen chemistry, it very readily abstracts F−, accepts an electron to form the stable radical cation S3N2+· and also dissociates completely in SO2 at r.t. This latter result is reflected in the results of 6-31G* calculations, which predict that S3N22+ is unstable with respect to SN+ and SNS+ by 400 kJ/mol in the gas phase with a small activation energy barrier. However, we estimate that S3N2(AsF6)2(s) is about 80 kJ/mol more stable than SNAsF6(s) and SNSAsF6(s), and owes its existence to the high lattice energy of the 2:1 salt. The identity of S3N2(AsF6)2 is also supported by vibrational spectroscopy and a normal coordinates analysis