The acid strength of the HF/AlX3 Lewis-Brønsted complexes involving various electron acceptors as ligands

The influence of tetrel bonds on the acidities of group 14 tetrafluoride - inorganic acid complexes

Ab initio methods were used to determine the influence of tetrel bond formation on the acidity. The systems composed of inorganic acids and tetrafluorides of 14 group elements have been tested - HA/EF₄ , where HA = H₂ O, NH₃ , HF, HCN, HNC, HCNO, HOCN and E = C, Si, Ge, Sn or Pb. It turns out that the electron density flow involved with formation of tetrel bond to carbon-based systems leads to negligible increase in acidity. In the case of the acceptor compounds based on the remaining 14 group elements however, the effect is much more apparent, as most of those compounds may be considered a Brønsted superacids. The electronic stability of anions formed after the deprotonation of aforementioned complexes has been investigated. Vast majority of the anions were found to exhibit significant electron binding energies.

Synthesis and Characterization of Tetrakis(pentafluoroethyl)aluminate

While perfluorinated aryl, aryloxy and alkoxy aluminum species are well-established as weakly coordinating anions (WCAs), corresponding perfluoroalkyl aluminum derivatives are virtually unknown. Reaction of Si(C2 F5 )3 CH3 with Li[AlH4 ] afforded the tetrakis(pentafluoroethyl)aluminate, [Al(C2 F5 )4 ]- . Several salts of the [Al(C2 F5 )4 ]- ion were synthesized and characterized by NMR spectroscopic methods, mass spectrometry, X-ray diffraction studies and elemental analysis.

Pentafluoroethylaluminates: A Combined Synthetic, Spectroscopic, and Structural Study

Salts of the tetrakis(pentafluoroethyl)aluminate anion [Al(C2 F5 )4 ]- were obtained from AlCl3 and LiC2 F5 . They were isolated with different counter-cations and characterized by NMR and vibrational spectroscopy and mass spectrometry. Degradation of the [Al(C2 F5 )4 ]- ion was found to proceed via 1,2-fluorine shifts and stepwise loss of CF(CF3 ) under formation of [(C2 F5 )4-n AlFn ]- (n=1-4) as assessed by NMR spectroscopy and mass spectrometry and supported by results of DFT calculations. In addition, the [(C2 F5 )AlF3 ]- ion was structurally characterized.

Superhalogens as Building Blocks of Super Lewis Acids

Lewis acids play an important role in synthetic chemistry. Using first-principle calculations on some newly designed molecules containing boron and organic heterocyclic superhalogen ligands, we show that the acid strength depends on the charge of the central atom as well as on the ligands attached to it. In particular, the strength of the Lewis acid increases with increasing electron withdrawing power of the ligand. With this insight, we highlight the importance of superhalogen-based ligands in the design of strong Lewis acids. Calculated fluoride ion affinity (FIA) values of B[C₂ BNO(CN)₃ ]₃ and B[C₂ BNS(CN)₃ ]₃ show that these are super Lewis acids.