The attempt to prepare hitherto unknown homopolyatomic cations of sulfur by the reaction of elemental sulfur with blue S8(AsF6)2 in liquid SO2/SO2ClF, led to red (in transmitted light) crystals identified crystallographically as S8(AsF6)2. The X-ray structure of this salt was redetermined with improved resolution and corrected for librational motion: monoclinic, space group P2(1)/c (No. 14), Z = 8, a = 14.986(2) A, b = 13.396(2) A, c = 16.351(2) A, beta = 108.12(1) degrees. The gas phase structures of E8(2+) and neutral E8 (E = S, Se) were examined by ab initio methods (B3PW91, MPW1PW91) leading to delta fH theta[S8(2+), g] = 2151 kJ/mol and delta fH theta[Se8(2+), g] = 2071 kJ/mol. The observed solid state structures of S8(2+) and Se8(2+) with the unusually long transannular bonds of 2.8-2.9 A were reproduced computationally for the first time, and the E8(2+) dications were shown to be unstable toward all stoichiometrically possible dissociation products En+ and/or E4(2+) [n = 2-7, exothermic by 21-207 kJ/mol (E = S), 6-151 kJ/mol (E = Se)]. Lattice potential energies of the hexafluoroarsenate salts of the latter cations were estimated showing that S8(AsF6)2 [Se8(AsF6)2] is lattice stabilized in the solid state relative to the corresponding AsF6- salts of the stoichiometrically possible dissociation products by at least 116 [204] kJ/mol. The fluoride ion affinity of AsF5(g) was calculated to be 430.5 +/- 5.5 kJ/mol [average B3PW91 and MPW1PW91 with the 6-311 + G(3df) basis set]. The experimental and calculated FT-Raman spectra of E8(AsF6)2 are in good agreement and show the presence of a cross ring vibration with an experimental (calculated, scaled) stretching frequency of 282 (292) cm-1 for S8(2+) and 130 (133) cm-1 for Se8(2+). An atoms in molecules analysis (AIM) of E8(2+) (E = S, Se) gave eight bond critical points between ring atoms and a ninth transannular (E3-E7) bond critical point, as well as three ring and one cage critical points. The cage bonding was supported by a natural bond orbital (NBO) analysis which showed, in addition to the E8 sigma-bonded framework, weak pi bonding around the ring as well as numerous other weak interactions, the strongest of which is the weak transannular E3-E7 [2.86 A (S8(2+), 2.91 A (Se8(2+)] bond. The positive charge is delocalized over all atoms, decreasing the Coulombic repulsion between positively charged atoms relative to that in the less stable S8-like exo-exo E8(2+) isomer. The overall geometry was accounted for by the Wade-Mingos rules, further supporting the case for cage bonding. The bonding in Te8(2+) is similar, but with a stronger transannular E3-E7 (E = Te) bonding. The bonding in E8(2+) (E = S, Se, Te) can also be understood in terms of a sigma-bonded E8 framework with additional bonding and charge delocalization occurring by a combination of transannular n pi *-n pi * (n = 3, 4, 5), and np2-->n sigma * bonding. The classically bonded S8(2+) (Se8(2+) dication containing a short transannular S(+)-S+ (Se(+)-Se+) bond of 2.20 (2.57) A is 29 (6) kJ/mol higher i...

Upon treating elemental sulfur with [AgSbF6], [AgAl(hfip)4], [AgAl(pftb)4] (hfip=OCH(CF3)2, pftb =OC(CF3)3) the compounds [Ag(S8)2][SbF6] (1), [AgS8][Al(hfip)4] (2), and [Ag(S8)2]+[[Al(pftb)4]− (3) formed in SO2 (1), CS2 (2), or CH2Cl2 (3). Compounds 1–3 were characterized by single‐crystal X‐ray structure determinations: 1 by Raman spectroscopy, 2 and 3 by solution NMR spectroscopy and elemental analyses. Single crystals of [Ag(S8)2]+[Sb(OTeF5)6]− 4 were obtained from a disproportionation reaction and only characterized by X‐ray crystal structure analysis. The Ag+ ion in 1 coordinates two monodentate SbF6− anions and two bidentate S8 rings in the 1,3‐position. Compound 2 contains an almost C4v‐symmetric {AgS8}+ moiety; this is the first example of an η4‐coordinated S8 ring (d(AgS)=2.84–3.00 Å). Compounds 3 and 4, with the least basic anions, contain undistorted, approximately centrosymmetric Ag(η4‐S8)2+ cations with less symmetric η4‐coordinated S8 rings (d(AgS)=2.68–3.35 Å). The thermochemical radius and volume of the undistorted Ag(S8)2+ cation was deduced as rtherm(Ag(S8)2+)=3.378+ 0.076/−0.120 Å and Vtherm(Ag(S8)2+)=417+4/−6 Å3. AgS8+ and several isomers of the Ag(S8)2+ cation were optimized at the BP86, B3LYP, and MP2 levels by using the SVP and TZVPP basis sets. An analysis of the calculated geometries showed the MP2/TZVPP level to give geometries closest to the experimental data. Neither BP86 nor B3LYP reproduced the longer weak dispersive AgS interactions in Ag(η4‐S8)2+ but led to Ag(η3‐S8)2+ geometries. With the most accurate MP2/TZVPP level, the enthalpies of formation of the gaseous [AgS8]+ and [Ag(S8)2]+ cations were established as ΔfH298([Ag(S8)2]+, g)=856 kJ mol−1 and ΔfH298([AgS8]+, g)=902 kJ mol−1. It is shown that the {AgS8}+ moiety in 2 and the {AgS8}2+ cations in 3 and 4 are the best approximation of these ions, which were earlier observed by MS methods. Both cations reside in shallow potential‐energy wells where larger structural changes only lead to small increases in the overall energy. It is shown that the covalent AgS bonding contributions in both cations may be described by two components: i) the interaction of the spherical empty Ag 5s0 acceptor orbital with the filled S 3p2 lone‐pair donor orbitals and ii) the interaction of the empty Ag 5p0 acceptor orbitals with the filled S 3p2 lone‐pair donor orbitals. This latter contribution is responsible for the observedlow symmetry of the centrosymmetric Ag(η4‐S8)2+ cation. The positive charge transferred from the Ag+ ion in 1–4 to the coordinated sulfur atoms is delocalized over all the atoms in the S8 ring by multiple 3p2→3σ* interactions that result in a small long‐short‐long‐short SS bond‐length alternation starting from S1 with the shortest AgS length. The driving force for all these weak bonding interactions is positive charge delocalization from the formally fully localized charge of the Ag+ ion.

S4(AsF6)2.AsF3 was prepared by the reaction of sulfur with arsenic pentafluroide in liquid AsF3 (quantitatively) and in anhydrous HF in the presence of trace amounts of bromine. A single-crystal X-ray structure of the compound has been determined: monoclinic, space group P2(1)/c, Z = 4, a = 7.886(1) A, b = 9.261(2) A, c = 19.191(3) A, beta = 92.82(1) degrees, V = 1399.9(4) A3, T = 293 K, R1 = 0.052 for 1563 reflections (I > 2 sigma (I) 1580 total and 235 parameters). We report a term-by-term calculation of the lattice potential energy of this salt and also use our generalized equation, which estimates lattice energies to assist in probing the homopolyatomic cation thermochemistry in the solid and the gaseous states. We find S4(AsF6)2.AsF3 to be more stable (delta fH degree [S4(AsF6)2.AsF3,c] approximately -4050 +/- 105 kJ/mol) than either the unsolvated S4(AsF6)2 (delta fH degree [S4(AsF6)2,c] approximately -3104 +/- 117 kJ/mol) by 144 kJ/mol or two moles of S2AsF6 (c) and AsF3 (1) by 362 kJ/mol. The greater stability of the S(4)2+ salt arises because of the greater lattice potential energy of the 1:2 solvated salt (1734 kJ/mol) relative to twice that of the 1:1 salt (2 x 541 = 1082 kJ/mol). The relative lattice stabilization enthalpies of M(4)2+ ions relative to two M2+ ions (i.e., in M4(AsF6)2 (c) with respect to two M2AsF6 (c) (M = S, Se, and Te)) are found to be 218, 289, and 365 kJ/mol, respectively. Evaluation of the thermodynamic data implies that appropriate presently available anions are unlikely to stabilize M2+ in the solid phase. A revised value for delta fH degree [Se4(AsF6)2,c] = -3182 +/- 106 kJ/mol is proposed based on estimates of the lattice energy of Se4(AsF6)2 (c) and a previously calculated gasphase dimerization energy of 2Se2+ to Se(4)2+.