The gas‐phase acidities ΔGacid(298 K) of the sulfanes H2Sn (n = 1–4) have been calculated by ab initio molecular orbital theory using the G2 and G2(MP2) methods, which were applied to the geometries of lowest energy. The results show that the higher sulfanes are surprisingly strong proton donors. The acidities (in kJ mol−1) are as follows: H2S (1444), H2S2 (1406), H2S3 (1370), H2S4 (1347). The latter three values may be compared to those of other strong Brønsted acids like gaseous HNO2 (1396), HCl (1371), and HBr (1332). The monoanions HSn− exhibit an interesting bond length distribution as a consequence of the charge delocalization by hyperconjugation, which in turn may be responsible for the high acidities of the sulfanes.

The relatively high stability and the structure of the simplest homoaromatic carbocation, the cyclobutenyl cation 1, was established ab initio by using correlated wave functions at HF 6–31G*, MP2(full)/6–31G*, MP2(full)/6–311G** and MP4(SDQ,full)/6–31G* geometries. The stability of 1 was estimated using homodesmotic and isodesmic reactions. The heat of formation of 1 was estimated to be 244 kcal mol−1 (1 kcal = 4·184 kJ). Chemical shift calculations were carried out at correlated levels and are in good agreement with the experimental values. At all levels of theory chemical shift calculations confirm the bent structure of 1. The MP4(SDTQ,fc)/6–311G**//MP2(full)/6–311G** + ZPE(MP2/(full)6–31G*), QCISD(T,fc)/6–31 + G*//MP2(full)/6–31G* + ZPE(MP2(full)/6–31G*) and MP4(SDQ,full)/6–31G*//MP4(SDQ,full)/6–31G* + ZPE(MP2(full)/6–31G*) ring inversion energies of 9·1, 9·3 and 9·0 kcal mol−1, respectively, agree with experiment (8·4 ± 0·5 kcal mol−1). Triplet electronic states are not competitive energetically. The homoaromatic character of the cyclobutenyl cation is shown by the nearly equal charges on C‐1, C‐2 and C‐3, the considerable 1,3‐bond order, the short 1·74 Å C‐1C‐3 distance and the large stabilization energy relative to the allyl cation.

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The gas‐phase geometries, dipole moments, enthalpies, and Gibbs free energies of dithionic acid H2S2O6, trithionic acid H2S3O6, tetrathionic acid H2S4O6, and disulfuric acid H2S2O7 have been determined by ab initio MO calculations at various levels of theory. The most stable conformations of H2S2O6 and H2S2O7 are of C2 symmetry, the other two acids are of C1 symmetry. The gas‐phase acidities defined as ΔG°298 of the deprotonation reaction obtained at the {MP2/6‐311++ G(3df, 3pd)//MP2/6‐31+ G(d) + ZPVE[HF/6‐31+ G(d)]} level are as follows [kJ·mol−1]: H2S2O6 1180, H2S3O6 1162, H2S4O6 1156, H2S2O7 1171. All four acids are much stronger than fluorosulfuric acid and chlorosulfuric acid in the gas phase. The decomposition of H2S2O7 into SO3 and H2SO4 is slightly endothermic and the same holds for the decomposition of H2S3O6 into SO3 and H2S2O3, but the reaction of H2S2O6 to SO2 and H2SO4 is strongly exothermic. The structures of the monoanions HS2O6−, HS3O6−, HS4O6−, and HS2O7− are characterized by intramolecular hydrogen bonds.

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In den Systemen N(n‐C4H9)OHSiO2H2O und N(i‐C5H11)4OHSiO2H2O wurde in kristallinen Silicatgemischen ein neuer, bisher unbekannter Silicatanionentyp nachgewiesen, der aus Doppelfünfringsilicatanionen der Formel [Si10O25]10− aufgebaut ist. Der entsprechende Trimethylsilylester [(CH3)3Si]10[Si10O25] wurde synthetisiert, seine Eigenschaften werden mitgeteilt.

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The gas‐phase geometries, dipole moments, enthalpies, and Gibbs free energies of thiosulfuric acid H2S2O3, peroxosulfuric acid H2SO5, fluorosulfuric acid HSO3F, and chlorosulfuric acid HSO3Cl as well as of their monoanions have been determined by ab initio MO calculations at various levels of theory. The most stable conformations of the four acid molecules are all of C1 symmetry. The acidities, defined as ΔG°298 of the deprotonation reaction, obtained by the G2 method are as follows [kJ mol−1]: HO−SO2−SH 1251 and HO−SO2−SH 1276, HO−SO(=S)−OH 1241, HO−SO2−OOH 1239, HO−SO2−F 1229, HO−SO2−Cl 1219. Good agreement of the calculated acidities of HSO3F and HSO3Cl is observed with the experimental gas‐phase acidities, which are the only experimental values available. The OH acidities of all five species are higher than that of sulfuric acid (1268 kJ mol−1). Therefore, these compounds may be termed as superacids. In contrast to the liquid state, chlorosulfuric acid is a stronger proton donor than fluorosulfuric acid in the gas phase. The dissociation of the acid molecules HSO3X (X = SH, OOH, F, Cl) into SO3 and HX is endothermic and endergonic in all cases. The same holds for the dissociation of the anions SO3X− into SO3 and X−. From these dissociation enthalpies and literature data the enthalpies of formation of the mentioned sulfonic acids and their anions are calculated.