Ab initio studies on the electronic structure and properties of aluminum hydrides that are analogues of boron hydrides

Although the boron hydrides are well-known in the literature, the aluminum hydride chemistry is limited to very few systems such as AlH(3), its dimer, and its polymeric form. In view of the recent experimental studies on the possible existence of the aluminum hydrides, herein, we have undertaken a systematic study on the electronic structure and properties of these aluminum hydrides. Under this, we have studied different classes of hydrides, viz., closo (Al(n)H(n+2)), nido (Al(n)H(n+4)), and arachno (Al(n)H(n+6)), similar to the boranes. All the aluminum hydrides are found to have exceptionally large highest-occupied molecular orbital-lowest-unoccupied molecular orbital gaps, low electron affinities, large ionization potentials and also large enthalpy and free energy of atomization. In addition, most of the structures are also found to have high symmetries. These exceptional properties can be indicative of the pronounced stability, and hence, it is expected that other aluminum hydride complexes can indeed be observed experimentally.     

Calculation of the properties of small boron and aluminum clusters

CNDO calculations were carried out for B _n and Al _n clusters, n=2–7, 12, and 13. The energetically most stable cluster structures were determined for each n. The results show that the stability of the more compact structures increases in going from boron to aluminum. We conclude that the CNDO model used is suitable for discerning the difference in the structure formation of boron and aluminum, which is manifest, in particular, in the formation of crystalline modifications by boron based on an icosahedral structural element, while crystalline aluminum has an FCC lattice.Institute of Theoretical and Applied Mechanics, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 5, pp. 48–54, September–October, 1989.     

Small atomic clusters: quantum chemical research of isomeric composition and physical properties

Structural Chemistry - In this review, we give a brief summary of methodological and computational aspects of determination of structure and different size-dependent properties of small atomic...     

Modern aspects of the chemistry of complex boron and aluminum hydrides

The review deals with new methods of synthesis of complex tetrahydroborates and tetrahydroaluminates and their coordination compounds, initial reagents for synthesis of borides, catalyst precursors, and materials for hydrogen economy.     

Transport properties of boron and aluminum

Transport cross sections and collision integrals are tabulated for a wide range of energies and temperatures for the interactions B–B and Al–Al. For aluminum, a semiclassical approximation was used to determine the scattering phase shifts from which the transport cross sections were calculated. For boron, the smaller reduced mass and the deep potential wells required the phase shifts at lower energies to be determined from a numerical solution of the time-independent Schroedinger equation; the semiclassical approximation was used at higher energies where the two methods agree. The variations of the collision integrals for viscosity and diffusion are presented graphically as a function of temperature. The results are applied to estimate the transport properties of gallium. Received: 9 July 1999 / Accepted: 18 August 1999 / Published online: 2 November 1999     

DFT study on the structural and electronic properties of Pt-doped boron nitride nanotubes

First-principles calculations based on density functional theory were carried out to investigate the structural and electronic properties of Pt substitution-doped boron nitride (BN) nanotubes. The electronic and structural properties were studied for substituted Pt in the boron and the nitrogen sites of the (BN) nanotube. The band gap significantly diminishes to 2.095 eV for Pt doping at the B site while the band gap diminishes to 2.231 eV for Pt doping at the N site. The band density increases in both the valence band and the conduction band after doping. The effects of the hardness and softness group 17 (halogen elements) were calculated by density functional theory (DFT).     

Ab initio and electron propagator theory study of boron hydrides

Boron hydrides (BH3, B2H6, B3H7, B4H10, B5H9, and B5H11) and their cations are studied by the coupled cluster CCSD(T) theory, the second-order Mller-Plesset (MP2) perturbation method, and the electron propagator theory in the partial third-order quasi-particle approximation, using the 6-311G(d,p) basis set. The vertical ionization potential energies are calculated, indicating an excellent agreement with the experimental data from photoelectron spectroscopy. Assignments to the experimental spectra are made on the basis of the present computational analyses. A significant Jahn-Teller effect on BH3+ leads to two states, 2A1 and 2B2, with the split energy of 0.14 eV. The triple and double B-H-B bridges are formed in B2H6+ and b-B3H7+, respectively. A new B-H-B bridge is formed while two B-B bonds are broken in B5H11+. The Jahn-Teller effect lowers the symmetry of B5H9 (C4v) to B5H9+ (C2) but slightly influences the structure of ara-B4H10 (C2v). The calculated properties of geometries, vibrational frequencies, and energies are compared with the experimental data available in the literatures.     

Relative thermodynamic stabilities of the isomeric dihydrofurans and isomeric dihydropyrans. An experimental and DFT study

The relative thermodynamic stabilities of 2,5-dihydrofuran (1) and 2,3-dihydrofuran (2), and of 3,4-dihydro-6H-pyran (3) and 3,4-dihydro-2H-pyran (4), were determined at several temperatures by base-catalyzed equilibration in DMSO solution. For 1 → 2, = –15.4±0.1 kJ mol⁻¹, =–12.6±0.5 kJ mol⁻¹, and =9.5±1.3 J K⁻¹ mol⁻¹ at 298.15 K. The second-law reaction enthalpy agrees with literature data based on calorimetric enthalpies of hydrogenation of the isomeric forms in hexane. For 3 → 4, =–19.3±0.2 kJ mol⁻¹, = –18.9±1.1 kJ mol⁻¹ and =1.1±3.0 J K⁻¹ mol⁻¹ at 298.15 K: the experimental reaction enthalpy is in marked disagreement with literature data based on estimation. On the other hand, both of the experimental reaction enthalpies of the present study are in good agreement with DFT calculations using the B3LYP functional and 6-311+G(2d,p) basis set.     

The electronic structure of the boron hydrides

In parts I and II of this series [1] it has been demonstrated that localized three centre and two centre bonds may be used as basic functions for molecular orbital calculations on closed (cage) and open (basket) boron polyhedral molecules. In the present paper it is shown that the face and edge matrices of this theory are related to incidal and 1 and 2 simplexial matrices in the same way that Hückel matrices in the theory of unsaturated hydrocarbons are related to incidal matrices and 0 and 1 simplexial matrices. The theory is thus a topologically-correct extension of Hückel theory to three dimensions.

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Zusammenfassung In Teil I und II dieser Serie [1] wurde demonstriert, da\ lokalisierte Dreizentren- und Zweizentren-Bindungen als Basisfunktionen für MO-Rechnungen bei geschlossenen (KÄfig) und offenen (Korb) polyhedralen Borwasserstoff-Molekülen benutzt werden können. In der vorliegenden Arbeit wird gezeigt, da\ die OberflÄchen- und Randmatrizen dieser Theorie mit Incidal- sowie 1- und 2-Simplexmatrizen verwandt sind, in derselben Art wie die Hückel-Matrizen in der Theorie der ungesÄttigten Kohlenwasserstoffe mit Incidal-Matrizen sowie 0- und 1-Simplexmatrizen in Beziehung stehen. Die Theorie ist somit eine topologisch korrekte Erweiterung der Hückel-Theorie auf drei Dimensionen.

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Résumé Dans les parties I et II de cette suite d'articles on a démontré que des liaisons localisées à trois et à deux centres peuvent Être employées comme fonctions de base pour des calculs d'orbitales moléculaires sur des molécules polyhédriques boriques fermées («cage») et ouvertes («panier»). Dans cet article on montre que les matrices «faces» et «arÊtes» de cette théorie sont liées aux matrices d'incidence et aux matrices Simplexes 1 et 2 de la mÊme manière que dans la théorie de Hückel la matrice hamiltonienne est reliée aux matrices d'incidence et simplexes 0 et 1. La théorie est donc une extension à trois dimensions, correcte du point de vue topologique, de la méthode de Hückel.

     

The electronic structure of the boron hydrides

The expansion of topological basis functions for tetrahedral and octahedral boron cage molecules in terms of an explicit atomic orbital basis is considered. A maximum localisation criteria is used to define mixing coefficients. The overlap between face basis functions in the two geometries is 0.79 and only a very crude parameter transferability exists. However, some aspects of the relative molecular orbital energy levels generated with a topological basis appear to be an improvement on those using an atomic orbital basis.

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Zusammenfassung Die Entwicklung topologischer Basisfunktionen nach einer expliziten Basis von Atomorbitalen für käfigförmige, tetraedrische und oktaedrische Moleküle, die Boratome enthalten, wird untersucht. Ein Kriterium maximaler Lokalisierung wird zur Bestimmung der Mischungskoeffizienten verwendet. Die Überlappung zwischen den Basisfunktionen, die zu den Seiten der beiden Geometrien gehören, beträgt 0,79, und es existiert nur eine ungefähre Übertragbarkeit der Parameter. Einige Aspekte der relativen MO-Energiewerte, die mit einer topologischen Basis gewonnen wurden, stellen eine Verbesserung gegenüber der Verwendung einer Atomorbitalbasis dar.

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Résumé Développement des fonctions de base topologiques en termes d'une base explicite d'orbitales atomiques pour des molécules cages de bore tétraédrique et octaédrique. Un critère de localisation maximum est utilisé pour définir les coefficients de mélange. Le recouvrement entre les fonctions de base faciales dans les deux geometries est de 0.79 et la transférabilité des paramètres n'est que très grossière. Cependant, certains aspects relatifs des niveaux d'énergie des orbitales moléculaires engendrées avec une base topologique apparaissent plus satisfaisants que ceux obtenus avec une base d'orbitales atomiques.

     

Some physical properties of compacted specimens of highly dispersed boron carbide and boron suboxide

Structure, shear modulus and internal friction (IF) of compacted specimens of boron carbide and boron suboxide have been investigated. Microtwins and stacking faults were observed along the {100} plane systems of polycrystalline specimens of boron carbide. Electrical conductivity of the specimens was that of p-type. Concentration of holes varied from 10¹⁷ to 10¹⁹ cm⁻³. The IF was measured in the temperature range 80-300 K. It was shown that the IF of boron carbide and that of boron suboxide were characterized with a set of similar relaxation processes. Mechanisms of the relaxation processes in boron carbide and boron suboxide are discussed in terms of the Hasiguti model of interaction between dislocations and point defects.     

Density functional study of small neutral and charged silver cluster hydrides

Small neutral, anionic, and cationic silver cluster hydrides AgnH and anionic HAgnH (n=1-7) have been studied using the PW91PW91 density functional method. It was found that the most stable structure of the AgnH complex (neutral or charged) does not always come from that of the lowest energy bare silver cluster plus an attached H atom. Among various possible adsorption sites, the bridge site is energetically preferred for the cationic and most cases of neutral Agn. For anionic Agn, the top site is preferred for smaller Agn within n相似文献   

A DFT study of isomeric conjugated,cross-conjugated and semi-conjugated six-membered heterocyclic mesomeric betaines

The structures and electronic properties of seven isomeric six-membered heterocyclic mesomeric betaines (HMBs) and four fully-covalent isomers have been calculated using B3LYP/6-311++G(p,d) methodology. The aromaticity indexes Bird I₆, HOMA, NICS(1) and aromatic stabilisation energy (ASE) have been calculated and compared. In agreement with an earlier study employing connectivity-matrix analysis, the previously unrecognised and little known semi-conjugated HMBs (Class 3) have calculated properties that are quite distinct from the isomeric conjugated HMBs (Class 1) and cross-conjugated HMBs (Class 2). In particular semi-conjugated systems have a higher degree of both classical and magnetic aromaticity than the isomers. In agreement with the calculated vertical ionisation potentials and electron affinities, the six-membered semi-conjugated species have high energy HOMOs and low energy LUMOs and these observations are consistent with the limited experimental data available. The results support the view that semi-conjugated rings should be recognised as a discrete class of dipolar heterocycle.     

Structure and properties of small silicon and aluminum clusters

Small Si_n and Al_n clusters (n = 3–10) were studied with the semiempirical molecular orbital method (MO) method SINDO1. For each n, various structures were optimized to determine the most stable structure. To obtain good qualitative agreement with available ab initio calculations d orbitals had to be omitted from the basis set. Both silicon and aluminum tend to build three-dimensional structures rather than two- or one-dimensional structures, except for n = 3 or 4. The structure growth was studied by approaching various sites of stable structures with one or more atoms. It was found that silicon and aluminum exhibit different structure growth, and consequently, different most-stable structures. Ionization potentials, HOMO -LUMO energy differences, binding energies per atom, and average atomic valencies are presented.     

Synthesis and characterization of new 19-vertex macropolyhedral boron hydrides

The new boron hydride anions 10-R-B19H19- (R = H, Thx) were synthesized by the reaction of M2[B18H20] (M = Na, K) with HBRCl.SMe2 (R = H, Thx) or HBCl2.SMe2 in diethyl ether. The anions are comprised of edge-sharing, nido 10- and 11-vertex cluster fragments, and are characterized by their 11B, 11B[1H], and 11B-11B COSY NMR spectra. The salt [(Ph3P)2N][B19H20].0.5THF crystallized in the triclinic space group P1 (a = 12.6344-(2) A, b = 13.5978(2) A, c = 14.1401(2) A; alpha = 77.402(2) degrees, beta = 81.351(2) degrees, gamma = 73.253(2) degrees). Possible synthetic pathways are discussed. The dianion B19H19(2-) is formed by deprotonation of B19H20- with Proton Sponge (1,8-bis(dimethylamino)naphthalene) in THF, and is identified on the basis of its 11B, 11B[1H], and 11B-11B COSY NMR spectra.     

The structure and luminescence of isomeric boron difluoride acetylnaphtholates

A comparative study of the fluorescence of solutions and crystals of isomeric boron difluoride acetylnaphtholates, 2-acetyl-1-naphtholate (1) and 1-acetyl-2-naphtholate (2), was performed. The compounds only differ in the position of the naphthyl group with respect to the chelate ring. An important role played by the stacking factor in the formation of the fluorescent properties of the complexes was revealed. The planar structure of the molecule and effective overlapping of the π systems of neighboring molecules of 1 cause a substantial bathochromic shift of its spectrum and a sharp increase in the intensity of excimeric fluorescence.     

The reaction of phenalenone with aluminum hydrides

Phenalenone 8 was reduced in refluxing ether with a series of aluminum hydrides. The product distribution in each reduction could be explained by initial 1,2- and 1,12-addition of hydride. Using the mixed chloraluminum hydrides, a high yield synthesis of phanalene 10 was discovered.