Na[GeF5]·2HF: the first quarternary phase in the H-Na-Ge-F system.

The structure of cis- or trans-bridged [GeF5]- anionic chains have been investigated [Mallouk et al. (1984). Inorg. Chem. 23, 3160-3166] showing the first crystal structures of µ-F-bridged pentafluorogermanates. Herein, we report the second crystal structure of trans-pentafluorogermanate anions present in the crystal structure of sodium trans-pentafluorogermanate(IV) bis(hydrogen fluoride), Na[GeF5]·2HF. The crystal structure [orthorhombic Pca21, a = 12.3786 (3), b = 7.2189 (2), c = 11.4969 (3) Šand Z = 8] is built up from infinite chains of trans-linked [GeF6]2- octahedra, extending along the b axis and spanning a network of pentagonal bipyramidal distorted Na-centred polyhedra. These [NaF7] polyhedra are linked in a trans-edge fashion via hydrogen fluoride molecules, in analogy to already known sodium hydrogen fluorides and potassium hydrogen fluorides.

The crystal structure of the ammonium salt of 2-aminomalonic acid.

The salt ammonium 2-aminomalonate (systematic name: ammonium 2-azaniumylpropanedioate), NH4+·C3H4NO4-, was synthesized in diethyl ether from the starting materials malonic acid, ammonia and bromine. The salt was recrystallized from water as colourless blocks. In the solid state, intramolecular medium-strong N-H...O, weak C-H...O and weak C-H...N hydrogen bonds build a three-dimensional network.

Synthesis and Structure of Protonated Sulfur Dioxide.

Salts of protonated sulfur dioxide were synthesized by recrystallization of [FS(OX)2][SbF6] (X=H, D) in aprotic solvents at low temperatures. Hemiprotonated sulfur dioxide [(SO2)2H][Sb2F11] was obtained from the solvent SO2 and the monoprotonated sulfur dioxide [OSOD][Sb2F11], using 1,1,1,2-tetrafluoroethane as solvent. For both compounds, single crystals were obtained and an X-ray structure analysis was conducted. Furthermore, the salts were characterized by Raman spectroscopy and the results were discussed together with quantum chemical calculations on the M06-2X/aug-cc-pVTZ level of theory.

Synthesis and Structure of the Small Superelectrophile [C2 (OH)2 Me2 ]2.

The acid-activation of 1,2-dicarbonyl compounds plays a key role in a variety of electrophilic reactions, some of which are only accessible in superacidic media when a superelectrophilic dication is formed. To obtain structural and electronic information about these elusive species, the vicinal dication [C2 (OH)2 Me2 ]2+ is synthesized and characterized by Raman spectroscopy and X-ray diffraction. Since this superelectrophile could not be stabilized in convenient superacids, the usage of liquid SO2 turned out to be crucial. The experimental data are discussed together with quantum-chemical calculations on the B3LYP/aug-cc-pVTZ level of theory. Natural Bond Orbital (NBO) analyses quantify the superelectrophilic interactions found in the solid state.

Two Roomtemperature-stable Trications - Triprotonated Triamino- and Tricyanobenzene.

Protonation of 1,3,5-tricyano- and 1,3,5-triaminobenzene was achieved in various superacidic media, resulting in the formation of the respective trinitrilium and triammonium species. Furthermore, the respective N-methyl nitrilium species was synthesized by methylation. Characterization was performed by NMR and vibrational spectroscopy, followed by single-crystal X-ray diffraction analyses of selected species. Fourfold protonation of the amine, which would have led to the triammonium arenium species, could not be achieved. Quantum chemical calculations are employed to enable full vibrational assignment as well to quantify charge localization.

Strengthening of the C-F Bond in Fumaryl Fluoride with Superacids.

The reaction of fumaryl fluoride with the superacidic solutions XF/MF5 (X=H, D; M=As, Sb) results in the formation of the monoprotonated and diprotonated species, dependent on the stoichiometric ratio of the Lewis acid to fumaryl fluoride. The salts [C4 H3 F2 O2 ]+ [MF6 ]- (M=As, Sb) and [C4 H2 X2 F2 O2 ]2+ ([MF6 ]- )2 (X=H, D; M=As, Sb) are the first examples with a protonated acyl fluoride moiety. They were characterized by low-temperature vibrational spectroscopy. Low-temperature NMR spectroscopy and single-crystal X-ray structure analyses were carried out for [C4 H3 F2 O2 ]+ [SbF6 ]- as well as for [C4 H4 F2 O2 ]2+ ([MF6 ]- )2 (M=As, Sb). The experimental results are discussed together with quantum chemical calculations of the cations [C4 H4 F2 O2 ⋅ 2 HF]2+ and [C4 H3 F2 O2 ⋅ HF]+ at the B3LYP/aug-cc-pVTZ level of theory. In addition, electrostatic potential (ESP) maps combined with natural population analysis (NPA) charges were calculated in order to investigate the electron distribution and the charge-related properties of the diprotonated species. The C-F bond lengths in the protonated dication are considerably reduced on account of the +R effect.

Ring Opening Reactions of ß-Propiolactam in Superacidic Media.

The reaction of ß-propiolactam in the superacidic systems HF/MF5 (M=Sb, As) led to the formation of monoprotonated 3-aminopropanoyl fluoride in the form of [C(O)F(CH2 )2 NH3 ][SbF6 ] and [C(O)F(CH2 )2 NH3 ][AsF6 ]. In the presence of traces of water, the diprotonated species ß-alanine [C(OH)2 (CH2 )2 NH3 ][AsF6 ]2 was synthesized for the first time. All salts were characterized by low-temperature infrared and Raman spectroscopy. Additionally, single-crystal X-ray analyses were conducted in the case of [C(O)F(CH2 )2 NH3 ][SbF6 ] and [C(OH)2 (CH2 )2 NH3 ][AsF6 ]2 . By using SO2 instead of HF as the solvent, the salt [C(OH)2 (CH2 )2 NHSO][SbF6 ]2 was obtained, and single-crystal X-ray analysis of this salt containing a thionylimide moiety was conducted. For the formation of these open-chain compounds, an acyl cationic species as intermediate is assumed, which is formed from N-protonated ß-propiolactam. Quantum chemical calculations at the B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVTZ levels of theory were carried out to gain a better understanding of the formation and the structural properties of protonated ß-propiolactam.

Protonated Ethylene Carbonate: A Highly Resonance-Stabilized Cation.

Salts containing the monoprotonated ethylene carbonate species of were obtained by reacting it with the superacidic systems XF/MF5 (X=H, D; M=Sb, As). The salts in terms of [C3 H5 O3 ]+ [SbF6 ]- , [C3 H5 O3 ]+ [AsF6 ]- and [C3 H4 DO3 ]+ [AsF6 ]- were characterized by low-temperature infrared and Raman spectroscopy. In order to generate the diprotonated species of ethylene carbonate, an excess of Lewis acid was used. However, this only led to the formation of [C3 H5 O3 ]+ [Sb2 F11 ]- , which was characterized by a single-crystal X-ray structure analysis. Quantum chemical calculations on the B3LYP/aug-cc-PVTZ level of theory were carried out for the [C3 H5 O3 ]+ cation and the results were compared with the experimental data. A Natural Bond Orbital (NBO) analysis revealed sp2 hybridization of each atom belonging to the CO3 moiety, thus containing a remarkably delocalized 6π-electron system. The delocalization is confirmed by a 13 C NMR-spectroscopic study of [C3 H5 O3 ]+ [SbF6 ]- .

Protonated Ethylene Carbonate: A Highly Resonance-Stabilized Cation.

Invited for this month's cover picture is the group of Prof. Andreas J. Kornath at the LMU in Munich (Germany). The cover picture shows the crystal structure of the salt of protonated ethylene carbonate [C3 H5 O3 ][Sb2 F11 ]. Protonated ethylene carbonate was synthesized by reacting the neutral compound in the superacidic system HF/SbF5 at low temperature. Interestingly, the single-crystal X-ray structure analysis revealed a planar CO3 moiety with nearly equal CO bond lengths. Further theoretical investigations of the cation led to the result, that it contains a remarkably delocalized 6π-electron system. On the cover this resonance stabilization is highlighted by p-orbitals on the CO3 moiety. Read the full text of their Research Article at 10.1002/open.202100229.

Protonation of γ-Butyrolactone and γ-Butyrolactam.

Invited for this month's cover is the group of Andreas Kornath at the Ludwig-Maximilian University of Munich (Germany). The cover picture shows the crystal structures of protonated γ-butyrolactone ([(CH2 )3 OCOH][AsF6 ]) and γ-butyrolactam ([(CH2 )3 NHCOH][AsF6 ]). Both salts were synthesized by reacting the neutral compounds in the superacidic system HF/AsF5 at low temperature. Interestingly, the X-ray structure analyses revealed not only structural parameters of the salts, but also the existent of C⋅⋅⋅F contacts in both species. Quantum chemical calculations were performed to investigate the nature of these contacts. Read the full text of their Full Paper at 10.1002/open.202000220.

Protonation of γ-Butyrolactone and γ-Butyrolactam.

γ-Butyrolactone and γ-butyrolactam were reacted in the superacidic systems XF/MF5 (X=H, D; M=As, Sb). Salts of the monoprotonated species of γ-butyrolactone were obtained in terms of [(CH2 )3 OCOH]+ [AsF6 ]- , [(CH2 )3 OCOH]+ [SbF6 ]- and [(CH2 )3 OCOD]+ [AsF6 ]- and the analogous lactam salts in terms of [(CH2 )3 NHCOH]+ [AsF6 ]- , [(CH2 )3 NHCOH]+ [SbF6 ]- and [(CH2 )3 NDCOD]+ [AsF6 ]- . The salts were characterized by low temperature Raman and infrared spectroscopy and for both protonated hexafluoridoarsenates, [(CH2 )3 OCOH]+ [AsF6 ]- and [(CH2 )3 NHCOH]+ [AsF6 ]- , single-crystal X-ray structure analyses were conducted. In addition to the experimental results, quantum chemical calculations were performed on the B3LYP/aug-cc-pVTZ level of theory. As in both crystal structures C⋅⋅⋅F contacts were observed, the nature of these contacts is discussed with Mapped Electrostatic Potential as a rate of strength.

Structures and Properties of trans-1,3,3,3-Tetrafluoro- propene (HFO-1234ze) and 2,3,3,3-Tetrafluoropropene (HFO-1234yf) Refrigerants.

The refrigerant trans-1,3,3,3-tetrafluoropropene (HFO-1234ze) is used as a replacement for former cooling agents that have been phased-out due to their global warming potential or ozone depleting potential. Although it is used on a large scale, only a few vibrational data and no structural data of HFO-1234ze are known. We report structure determinations based on low-temperature single-crystal X-ray diffraction data as well as gas-phase diffraction data of HFO-1234ze and HFO-1234yf (2,3,3,3-tetrafluoropropene). Furthermore, vibrational spectra of HFO-1234ze in all phases are described. The results are discussed together with quantum-chemical calculations on the PBE0/cc-pVTZ level of theory. Combustion experiments of HFO-1234ze show carbonyl difluoride, carbon dioxide and hydrogen fluoride to be the main combustion products.

Tuning the Anomeric Effect in Sulfamide with Superacids.

This study shows that the anomeric effect (negative hyperconjugation) that arises in sulfamide, as a result of the relatively short S-N bonds, can be tuned by the utilization of superacidic media. Sulfamide was reacted in binary superacidic systems XF/MF5 (M=As, Sb; X=H, D) and HF/BF3 . The colorless salts formed, [X2 NSO2 NX3 ]+ [MF6 ]- and [H2 NSO2 NH3 ]+ [BF4 ]- were characterized by low-temperature vibrational spectroscopy. In the case of [H2 NSO2 NH3 ]+ [BF4 ]- , a single crystal X-ray diffraction study was performed. The salt crystallizes in the monoclinic space group P21 /c with four formula units per unit cell. An exclusive N,N'-diprotonation was observed in the superacidic system HF/SbF5 when using several equivalents of the Lewis acid. Low-temperature vibrational spectra as well as a single-crystal X-ray structure of [H3 NSO2 NH3 ]2+ 2 [SbF6 ]- ⋅2 HF are reported. The salt crystallizes in the orthorhombic space group Pna21 with four formula units per unit cell. Upon mono- or diprotonation of sulfamide, remarkable structural changes of the sulfur-nitrogen bond lengths were observed. Herein, these changes are discussed together with quantum chemical calculations.

The Existence of Tricyanomethane.

Calcium tricyanomethanide reacts with hydrogen fluoride under formation of tricyanomethane and Ca(HF2)2. Tricyanomethane is stable below -40 °C and was characterized by IR, Raman, and NMR spectroscopy. The vibrational spectra were compared to the quantum-chemical frequencies at the PBE1PBE/6-311G(3df,3dp) level of theory and confirm the predicted C(3v) symmetry of the molecule with regular C-H (109.8 pm), C-C (146.7 pm), and C≡N (114.7 pm) bonds.

The protonation of HSO(3)F: preparation and characterization of fluorodihydroxyoxosulfonium hexafluoroantimonate [H(2)SO(3)F](+)[SbF(6)](-).

Sulfurtrioxide reacts with the superacidic solutions XF/SbF(5) (X=H, D) to form the corresponding salts [X(2)SO(3)F](+)[SbF(6)](-), which are the protonated forms of fluorosulfuric acid. The salts have been characterized by vibrational spectroscopy and a single-crystal structure analysis. [H(2)SO(3)F](+)[SbF(6)](-) crystallizes in the monoclinic space group P2(1)/n (no. 14) with four formula units in the unit cell. The crystal structure possesses a distorted tetrahedral O(3)SF skeleton of the cations, which are linked with two strong hydrogen bridges to [SbF(6)](-) anions and forms a one-dimensional chain. The crystal structure and the vibrational spectra are compared to the quantum-chemical-calculated free [H(2)SO(3)F](+) cation. Additionally, an [H(2)SO(3)F(HF)(2)](+) unit was calculated at the RHF/6-311(++)G(d,p) level to simulate HF hydrogen bridges found in the solid state.