Ab Initio Study of the AlX₃···2H₂O (X = F, Cl) and AlF₃···3H₂O Complexes

Abstract

The structures, binding energies, and harmonic vibrational frequencies of AlX3···2H2O (X = F,Cl) complexes have been explored for the first time at the HF, DFT, and MP2 levels using the 6-31G*, 6-31+G*, and the 6-311G** basis sets. The optimizations were performed without symmetry restrictions or other structural limitations. All complexes investigated were found to be energetically stable, regardless of the computational method used. The calculations showed that the DFT(B3LYP)/6-31+G* method is suitable for the prediction of both binding energies and vibrational frequencies for these types of complexes. This makes possible qualitatively accurate calculations at a relatively low computational expense of even larger, comparable complexes. The AlF3···3H2O complex was therefore investigated only at this level, yielding the basis for the molecular interpretation of the first steps of the macroscopically investigated hydration process of AlF3. A comparison of the binding energies of complexes containing an increasing number of water molecules has been performed. Furthermore, the vibrational frequencies of all complexes have been predicted.

Ultrathin Multifunctional Oxide Coatings for Lithium Ion Batteries

“…That might also help explain why the capacity of Al 2 O 3 /Si is lower under constant current comparing with the level of the uncoated one in our case, and eventually it increases close to the uncoated one after a few cycles. One possible mechanism of the AlF 3 /Al 2 O 3 formation is the reaction of PF 5 resulting from the decomposition of LiPF 6 (as shown in Equation 2) with trace water leading to HF which further reacts with Al 2 O 3 and forms AlF 3 ·3H 2 O 27, 28…”

Possible Formation of H3O+ Cations Due to Aluminum Fluoride Interactions with Water

“…Although the relative energies of the AlF 3 ·3H 2 O­( 4 ) and AlF 3 ·3H 2 O­( 5 ) isomers are relatively small (2.8 and 3.2 kcal/mol, respectively), such structures should not be present in considerable amounts at room temperature. Interestingly, the earlier studies reported the stability of only one isomeric structure of AlF 3 ·3H 2 O, which corresponds to the isomer AlF 3 ·3H 2 O­( 4 ) shown in Figure , whereas the kinetic stability of lower energy structure AlF 3 ·3H 2 O­( 1 – 3 ) was not predicted. , Finally, the sixth isomer of AlF 3 ·3H 2 O (labeled AlF 3 ·3H 2 O­( 6 ) in Figure ) we found in the 0–20 kcal/mol energy range, exhibits a completely different structure, mostly due to the presence of the H 3 O fragment. It consists of the quasi tetrahedral AlF 3 OH fragment connected to the H 2 O···H 3 O moiety via the hydrogen bonds.…”

“…The structure 2 indicates the presence of only one O → Al dative bond; however, the additional stabilization is provided by the formation of hydrogen bond between the two H 2 O molecules localized on the same site of the AlF 3 pyramid. It should be noted that earlier studies reported only one isomeric structure of AlF 3 ·2H 2 O, which corresponds to the AlF 3 ·2H 2 O­( 2 ) isomer, whereas the existence of the global minimum AlF 3 ·2H 2 O­( 1 ) consisting of a planar AlF 3 fragment forming two dative bonds with water molecules was overlooked . The structure of the third AlF 3 ·2H 2 O isomer (labeled 3 in Figure ) is very different and consists of the H 3 O fragment H-bonded to the remaining AlF 3 OH moiety.…”

“…Theoretical studies of the hydration processes of AlF 3 are rather sparse and seem incomplete (i.e., limited to the most stable AlF 3 hydrates). Moreover, the quantum chemical calculations (using Hartree–Fock, Møller–Plesset (MP) or density functional methods) have been performed only for the AlF 3 complexes with one, two, or three water molecules. − Namely, (i) Ball determined (at the MP2/6-31G­(d,p) level) the gas phase equilibrium structure of the AlF 3 H 2 O in which the presence of two H-bonds was revealed; (ii) Scholz et al found three isomers of AlF 3 ·3H 2 O (by performing the B3LYP/6-31+G­(d) calculations) whose structures indicated the formation of either one or two H 2 O → AlF 3 dative bonds; (iii) Krossner et al evaluated binding energies for selected geometries (that were believed to be the global minima) of the AlF 3 ·2H 2 O and AlF 3 ·3H 2 O complexes . Even though it seems obvious that the presence of at least 5–6 water molecules should be taken into account while theoretically studying the hydration processes of AlF 3 , such calculations have not been undertaken thus far.…”

Aluminum Fluoride‐Supported Platinum and Palladium as Highly Efficient Catalysts of n‐Pentane Hydroisomerization

“…Larger quantities of water (in polyhydrated aluminum fluoride) would also not function for this purpose because of a relatively stable extensive hydrogen bonding at the active sites. [46] XPS studies of Makarowicz et al showed that handling of freshly fluorinated HS-AlF 3 under a protecting Ar atmosphere and in a glovebox exposes the samples to higher humidity levels, so that Lewis sites are probably readily covered with OH or H 2 O surface species. [47] However, the authors argue that these Brønsted acid species should be removed by treatment at higher temperature before HS-AlF 3 reagents can fully develop their Lewis acidity.…”