[en] Using the CCSD/6-311++G(d,p) method calculations of LiHF₂, NaHF₂, and KHF₂ molecules are realized. By the AIM method it is shown that hydrogen bond in LiHF₂, NaHF₂, and KHF₂ molecules differ from ordinary one and is similar to covalent interaction

[en] A search of the Cambridge Structural Database (CSD, version 5.05, 1993) was performed in order to compare the geometrical features of the hydrogen bonds involving on the one hand amino groups and on the other hand carboxylates, sulfonates or monohydrogen phosponates. Phosphonates were not considered because only four entries containing amino and phosphonate moieities were located in the CSD. The hydroxylic group of monohydrogen phosphonates primarily acts as a hydrogen-bond donor. The three moieties under study show NH..O hydrogen bonds with similar geometrical features. This statistical analysis has focused on the hydrogen-bond distances and angles and on the distributions of the H atoms around the acceptor O atoms of carboxylates, sulfonates or monohydrogen phosphonates. (orig.)

[en] Highlights: • The hexagonal boron cluster B₆⁴⁺ is a good new noble gas trapper. • The NgB bonds in the monocyclic compounds B₆Ng_n⁴⁺(n = 0–6) are covalent bonds and can be represented as the donor-acceptor model. • The NICS analysis shows that the hexagonal boron-noble gas compounds B₆Ng_n⁴⁺(n = 0–6) are typically aromatic systems. The hexagonal boron-noble gas compounds B₆Ng_n⁴⁺ (n = 1–6, Ng = HeRn) have been studied theoretically. The geometry, bond energies and thermodynamics properties are reported. For ArRn, the BNg bond length is close to the sum of the covalent radii of B and Ng, the BNg average bond energy is large up to 59.61–169.43 kcal/mol. There is large charge transfer from Ng to the boron ring, the Ng → boron σ-donation originating from the interaction between the valence p orbital of Ng and the LUMO of the boron ring is the predominant contribution towards the NgB bond stabilization. The NICS analysis shows that B₆Ng_n⁴⁺ have aromaticity.

[en] Highlights: • The B3LYP, B3PW91, and M06-2X computational methods were used. • The theoretical observations demonstrate that only sterically bulky substituents can greatly stabilize the triply bonded RAlPR molecules. • These conclusions are based on both the thermodynamic and the kinetic viewpoints. The effect of substitution on the potential energy surfaces of triple-bonded RAlPR (R = F, OH, H, CH₃, SiH₃, SiMe(SitBu₃)₂, SiiPrDis₂, Tbt (C₆H₂-2,4,6-{CH(SiMe₃)₂}₃), and Ar^∗ (C₆H₃-2,6-(C₆H₂-2,4,6-i-Pr₃)₂)) compounds was investigated by using the theoretical methods (i.e., M06-2X/Def2-TZVP, B3PW91/Def2-TZVP, B3LYP/LANL2DZ+dp, and CCSD(T)). The theoretical examinations reveal that all of the triple-bonded RAlPR species prefer to adopt a bent form with a roughly perpendicular bond angle ($\angle$Al–P–R). In addition, the theoretical evidence demonstrates that only the bulkier substituents can efficiently stabilize the central AlP triple bond. Moreover, the theoretical analyses (the natural bond orbital, the natural resonance theory, and the charge decomposition analysis) indicate that the bonding characters of the triply bonded RAlPR molecules should be described as R′AlPR′. That is to say, the AlP triple bond contains one conventional σ bond, one conventional π bond, and one donor-acceptor π bond. Nevertheless, the theoretical conclusions based on the poor overlap populations between Al and P elements suggest the AlP triple bond in such an acetylene analogues (RAlPR) is likely to be very weak.

No abstract available

[en] Neutron diffraction studies have led to the precise determination of H-atom positions in 18 crystalline α-amino acids. These structures are all stabilized by three-dimensional networks of H-bonds and significant differences occur among corresponding bond distances and angles for those groups involved in H-bonding. Specifically, there is a good inverse correlation between N-H and H...O distances for N-H...O bonds. (Auth.)

[en] Elasticity of structural complexes in sulfates, chromates, and molybdates of uranyl was investigated quantitatively using available data on U-O_br-T (O_br - bridge oxygen atom; T=S, Cr, Se, Mo) bond angles and T-O bond lengths. Only structural complexes with vertex bond between coordination polyhedrons UO_n (n=6, 7) and TO₄ tetrahedrons were considered. Analysis of distribution of U-O_br-T bond angle values indicated on raised elasticity of U-O_br-Mo in comparison with sulfates and chromates. This fact defined greater structural variability of uranyl molybdates and possibility of skeleton structures building up

[en] A survey of the geometry and environment of water molecules in crystalline hydrates is presented. Histograms and correlation analyses are based on 97 crystal structures accurately determined by neutron diffraction, and include data from 183 water molecules, each donating two hydrogen bonds. The sample is analyzed according to the nature of the hydrogen-bond acceptors and of the coordinated cations. Cases of bifurcated hydrogen bonds are also discussed. The hydrogen bonds tend to be linear and the acceptors tend to be located close to the water plane. The tendency of coordination bonds to be collinear with the direction of one of the lone pairs of the O or their bisector increases with the strength of the bonds. The length of the W-H bond, which, on average, is shorter than in the gas phase, is correlated to the strength of the donated hydrogen bond and to the nature of the acceptor as well as to the type of coordination. On average, W-H is shorter for weaker hydrogen bonds, lower electronegativity of the acceptors and a triangular (as opposed to tetrahedral) type of coordination. The H-W-H angle is, on average, about 2.5⁰ wider than in the gas phase; this widening is correlated to the type of coordination (larger for triangular), to the strength of the hydrogen bond, and to the A...W...A angle between acceptors. Differences between the dimensions of water molecules in gas and solid phases are shown to be effective and not due to uncorrected thermal effects. (Auth.)

[en] Intermetallic compounds represent an extensive pool of candidates for energy related applications stemming from magnetic, electric, optic, caloric, and catalytic properties. The discovery of novel intermetallic compounds can enhance understanding of the chemical principles that govern structural stability and chemical bonding as well as finding new applications. Valence electron-poor polar intermetallics with valence electron concentrations (VECs) between 2.0 and 3.0 e^–/atom show a plethora of unprecedented and fascinating structural motifs and bonding features. Furthermore, establishing simple structure-bonding-property relationships is especially challenging for this compound class because commonly accepted valence electron counting rules are inappropriate.

[en] Interaction of phosphoryl chloride (POCl₃) with CH₂Cl₂ and CCl₄ has been studied using matrix isolation infrared and ab initio computations. Computations performed at MP2 level of theory using aug-cc-pVDZ basis set indicated a 1:1 phosphorus bonding interaction for the POCl₃-CH₂Cl₂ and POCl₃-CCl₄ and the heterodimers are generated at low temperature in N₂ and Ar matrixes and characterized using infrared spectroscopy. The multifaceted interaction characteristics were further analyzed using NBO, AIM and EDA analyses. (author)