Structure, stability and vibrational spectrum of the hydrogen-bonded complex between HNO3 and H2O. Ab initio and DFT studies

The structure, stability and vibrational spectrum of the binary complex between HONO2 and H2O have been investigated using ab initio calculations at SCF and MP2 levels with different basis sets and B3LYP/6-31G(d,p) calculations. Full geometry optimization was made for the complex studied. It was established that the hydrogen-bonded H2O...HONO2 complex has a planar structure. The corrected values of the dissociation energy at the SCF and MP2 levels and B3LYP calculations are indicative of relatively strong OH...O hydrogen-bonded interaction. The changes in the vibrational characteristics (vibrational frequencies and infrared intensities) arising from the hydrogen bonding between HONO2 and H2O have been estimated by using the ab initio calculations at SCF and MP2 levels and B3LYP/6-31G(d,p) calculations. It was established that the most sensitive to the complexation is the stretching O-H vibration from HONO2. In agreement with the experiment, its vibrational frequency in the complex is shifted to lower wavenumbers. The predicted frequency shift with the B3LYP/6-31G(d,p) calculations (-439 cm(-1)) is in the best agreement with the experimentally measured (-498 cm(-1)). The intensity of this vibration increases dramatically upon hydrogen bonding. The ab initio calculations at the SCF level predict an increase up to five times; at the MP2 level up to 10 times and the B3LYP/6-31G(d,p) predicted increase is up to 17 times. The good agreement between the predicted values of the frequency shifts and those experimentally observed show that the structure of the hydrogen-bonded complex H2O...HONO2 is reliable.     

KNa2Tm[Si8O19] · 4H2O,a new layered silicate related to rhodezite-shlykovite-delhayelite-umbrianite-guenterblassite-hilleshaymite: Topology-symmetry analysis of the OD-family and structure prediction

Crystals of a new silicate KNa₂Tm[Si₈O₁₉] · 4H₂O, space group P12/m1 (the chemical formula was determined in the course of structure solution), are obtained under hydrothermal conditions. KNa₂Tm[Si₈O₁₉] · 4H₂O is the first synthetic representative of the family, which contains the following well-known and recently discovered minerals: rhodezite, delhayelite (fivegite, hydrodelhayelite), mountainite, shlykovite (cryptofillite), and guenterblassite (umbrianite, hilleshaymite). A crystal chemical analysis within the extended OD theory revealed the similarity of the structures of the family, including the new simplest representative and the factors responsible for structural diversity, namely, different symmetry of sheets of octahedra connected with layers of tetrahedra, which are distinguished in all the structures, and different patterns of symmetry relation between the sheets. Hypothetic structures with a higher degree of disordering are deduced. Crystals with these structures can be found in nature or obtained synthetically.     

Proton‐stabilized three‐dimensional anionic framework in H[Zn6O2(BO3)3]

A three‐dimensional anionic framework built up from [ZnO₄] tetra­hedra and planar [BO₃] groups, stabilized by H atoms, has been found for hydrogen zinc oxide borate, H[Zn₆O₂(BO₃)₃]. Boron and one of the borate O atoms are on 18e (2) positions. Triple units of [ZnO₄] tetra­hedra sharing a common oxygen vertex on a 12c (3) site and strong asymmetrical linear hydrogen bonds with the H atom [on a 12c (3) position] disordered over a twofold axis are specific structural features of this zincoborate. There is evidence that the reported Zn₄O(BO₃)₂ [Harrison, Gier & Stuky (1993). Angew. Chem. Int. Ed. Engl. 32 , 724–726] corresponds to this structure.     

Chromatographic effect during the preparation of supported two-component catalysts by impregnation

The reason for variation in the granule depth of the component ratio in supported two-component catalysts during their preparation has been studied. This phenomenon, which may be called chromatographic effect, depends on the different affinities between substrate and ions in the impregnating solution. The model system chosen is CuCo₂O₄/Al₂O₃. It has been established that after modification of the support with Cu²⁺ ions, the stoichiometric CuCo₂O₄ phase is formed. The catalysts obtained have an enhanced activity.