A computational investigation of 11B electric field gradient and chemical shielding tensors as well as NBO analysis in the B80 fullerene

Using first-principles calculations within the frame of the density functional theory, we analyze electronic properties of the boron fullerene B80, based on NMR, NQR parameters and NBO analysis. Our results show three typical ranges for boron chemical shielding parameters corresponding to each of the nonequivalent magnetic sites of the B atoms. These three sites are related to frame atoms and two sets of atoms capping hexagons, endohadral and exohedral caps. Calculating quadrupole coupling components confirm this conclusion with more sensitivity than chemical shielding parameters. In addition calculated asymmetry parameter shows that EFG tensor for boron atoms capping hexagons is axially symmetric, η ≈ 0, while this tensor becomes considerably asymmetric for frame atoms, η = 0.95, as a result of charge transfer from 20 boron atoms capping hexagons to the 60 frame atoms.     

Sulfur Atoms as Ligands in Metal Complexes

The types of sulfur bonding—as sulfane or sulfide—encountered in the molecules of maingroup elements are almost unknown in the chemistry of metal complexes, where the sulfur atoms function instead as two-electron donors by bridging two metal atoms, as four-electron donors by bridging three or four metal atoms, or as six-electron donors by incorporation between four metal atoms. In such complexes, the metal-metal bond can be modified over a wide range by chemical or electrochemical variation of the number of electrons present. The readiness with which polynuclear complexes containing metals and sulfur undergo redox reactions is also utilized by Nature in the active sites of some redox proteins.     

Clusters as crystal fragments of silicon bulk

Silicon clusters of 13 to 43 atoms were studied with the semi-empirical method SINDO1. Crystalline structures of face-centered cubic (fcc), hexagonal close packed (hcp) and diamond type and noncrystalline structures of icosahedral type were compared. Noncrystalline structures are most stable for clusters up to 13 atoms. Clusters with 19 and more atoms of the fcc structure are preferable to the less dense diamond structure. With more than 35 Si atoms, the diamond structure is favored over the hcp structure. The binding energy of fcc and hcp structures decreases and that of the diamond structure increases with increasing cluster size. A similar trend is observed for the HOMO-LUMO energy gap which is taken as a measure of the band gap.     

Basis-Modified hydrogen atoms as embedding atoms in ab initio chemisorption cluster model calculations on Si surfaces

A comparative and systematic ab initio study of different models simulating the Si (111) surface has been carried out for a variety of embedding hydrogen atoms including unmodified hydrogen atoms and modified hydrogen atoms described with a STO-4G basis set and a Slater exponent optimized to have the cluster atoms as neutral as possible. The study has been extended to some chemisorption processes as Ag and Al on Si (111). The main conclusion of the present work is that neither the electronic structure of the isolated cluster models nor the nature of the chemisorption bond depend on the kind of embedding hydrogen atoms used to saturate the free valences of the cluster edge atoms. © John Wiley & Sons, Inc.     

Variable connectivity index as a tool for modeling structure-property relationships

We report on the calculation of normal boiling points for a series of n = 58 aliphatic alcohols using the variable connectivity index in which variables x and y are used to modify the weights on carbon (x) and oxygen atoms (y) in molecular graphs, respectively. The optimal regressions are found for x = 0.80 and y = -0.90. Comparison is made with available regressions on the same data reported previously in the literature. A refinement of the model was considered by introducing different weights for primary, secondary, tertiary, and quaternary carbon atoms. The standard error in the case of the normal boiling points of alcohols was slightly reduced with optimal weights for different carbon atoms from s = 4.1 degrees C (when all carbon atoms were treated as alike) to s = 3.9 degrees C.     

Mass spectrometry as a diagnostic tool for 5-hydroxysteroids

The mass spectra of twelve 5-hydroxysteroids (1–12), indicate that a common feature is the formation of the ion a by loss of the four ring A C atoms 1, 2, 3, and 4, with the H atoms and other substituents attached.     

An inertial model of atoms: atomic spectra as a resonance problem

A new model of atoms based on the theory of material waves is proposed. Atoms are characterized by an inertial aggregation of negative charge within the atomic shell, the calculation yields, for hydrogen atoms, an atomic radius of 0.470 nm. Atomic spectra result from radial material waves, quantization being the consequence of boundary conditions imposed on the fundamental wave equation. Stark effects and Zeeman effects are treated in detail, they are referred to deformations and rotations of the atomic shell. An analysis of Stern--Gerlach experiments bases subsequent deflections of single atoms on rotations and interactions of magnetic fields.     

The Pentazadienide Ion as a Ligand in Metal Complexes

The pentazadienide ion is a surprisingly versatile ligand. The planar, zigzag N₅ chain can utilize its atoms N1, N3, and N5 to complex one, two, or three metal atoms in a monodentate or bidentate fashion. Of particular interest is the ligand's ability to promote short metal-metal contacts in complexes with d¹⁰ metal ions.     

Application of solid-state early-transition metal clusters as catalysts

Metal cluster compounds are expected to be catalysts for new reactions because of synergistic effect of the metal atoms. In solid-state halide clusters and sulfide clusters, metal cluster frameworks are linked in two- or three-dimensions to form a cluster network. Halogen- or sulfur-deficient metal sites in an octahedral metal cluster framework are retained intact and act as catalytically active sites even at high temperatures of 400–700?°C. This review reports recent advances in the development of coordinatively unsaturated metal atoms on solid-state clusters with an octahedral metal framework and their application to organic catalytic reactions.     

Computational study of aza-adamantanes as multivalent bases

Structure and bonding characteristics, and gas phase stepwise basicities of proposed multivalent bases 1,3,5,7-tetraazatricyclo[3.3.1.1(3,7)]decane, 1,3,5,7,9,10-hexaazatricyclo[3.3.1.1(3,7)]decane and tricyclo[3.3.1.1(3,7)]azadecane, named and abbreviated here respectively as tetra-aza-adamantane (TAA), hexa-aza-adamantane (HAA) and deca-aza-adamantane (DAA), have been studied using B3LYP/6-311++G** method. Effects of protonation on the bond lengths and angles, and atomic charges, and on their correlations are studied in detail. Results show that the most affected characteristics by protonation are the N–H bond lengths and the charge of the hydrogen atoms. It is found, interestingly, that in the protonation of DAA, electric charges of the unprotonated nitrogen atoms are increased more than that of the protonated nitrogen atoms. Because of very small effects of protonation on the skeletal C–N and N–N bond lengths, it can be said that the aza-adamantane cage volume is not changed significantly upon protonation. The protonation energies approve multivalent nature of these bases with the order of TAA ≈ HAA > DAA. Different isomers for the unprotonated and protonated HAA and DAA are also studied.     

Distorted bcc indium cubes as structural motifs in Ca

The title compounds were prepared from the elements by reactions in water-cooled glassy carbon crucibles under an argon atmosphere in a high-frequency furnace. CaPdIn4 crystallizes with the YNiAl4-type structure: Cmcm, a=446.7(3), b=1665(1), c=754.3(5) pm, wR2=0.0465 with 646 F2 values and 24 variables. The structure is built up from a complex three-dimensional [PdIn4] polyanion in which the calcium atoms occupy distorted pentagonal tubes formed by indium and palladium atoms. CaRhIn4 and CaIrIn4 adopt the LaCoAl4-type structure: Pmma, a=867.6(1), b=422.91(8), c=745.2(1) pm, wR2=0.0583 with 468 F2 values and 24 variables for CaRhIn4; a=869.5(1), b=424.11(6), c=746.4(1) pm, wR2= 0.0614 471 F2 values with 24 variables for CaIrIn4. This structure type, too, has a three-dimensional [RhIn4] polyanion which is related to the structure of binary RhIn3. The calcium atoms fill distorted pentagonal prismatic channels formed by indium atoms. Semi-empirical band structure calculations for Ca-RhIn4 and CaPdIn4 reveal strongly bonding In-In, Rh-In and Pd-In interactions but weaker Ca-Rh, Ca-Pd and Ca-In interactions. CaRhIn4 and Ca-PdIn4 are compared with other indium-rich compounds such as YCoIn5 and Y2CoIn8, and with elemental indium. Common structural motifs of the indium-rich compounds are distorted bcc-like indium cubes.     

Structural study of highly halogenated dihydropyridine derivatives as potential calcium channel modulators

Two dihydropyridines endowed with fluorine atoms ( 3 ) and fluorine and chlorine atoms ( 4 ) have been synthesized and structurally characterized by experimental X‐ray analyses and theoretical calculations at the semiempirical (AMI) and ab initio (HF/6–31G*) levels. The results show that these compounds meet the required criteria to act as potential calcium channel modulators.     

Density Functional Theory Study on La Complex with Schiff-base as Building Block

1 INTRODUCTION Recently, there has been a growing interest[1~5] inlanthanon complexes because of their abundant stru-ctural characters and important biologic activities.The complexes are extensively used as coordinationand stabilization agents[6, 7] for the measures of me-tallic ions, antibacterial and anticancer drugs[8], cata-lysts for vitamin B6 in amination and oxidation re-actions[9], biological models of N2, O2 carriers andaminophenol asymmertry synthesis and preparationof nonprote…     

Monolayer boron-arsenide as a perfect anode for alkali-based batteries with large storage capacities and fast mobilities

We investigate, by means of first-principles density functional theory (DFT) calculation, the possibility of using hexagonal boron-arsenide (h-BAs) as an anode material for alkali-based batteries. We show that the adsorption strength of alkali atoms (Li, Na, and K) on h-BAs in comparison with graphene and other related materials changes a little as a function of alkali atom concentration. When the separation between alkali atoms and h-BAs is less than the critical distance of ~5 Å, the adsorption energy abruptly increases showing fast adsorption without an energy barrier. Furthermore, the low energy barriers of 0.322, 0.187, and 0.0.095 eV for Li, Na, and K, respectively, ensure the fast ionic diffusivities for all the three alkali atoms. Additionally, the addition of these alkali atoms transforms the electronic properties of h-BAs from semiconducting to metallic, resulting in improved electronic conductivities. Most interestingly, the excellent storage capacities of h-BAs (~626 mAh/g) for alkali atoms make it a material of similar caliber to that of other popular anode materials. Finally, the average open circuit voltages are calculated and found to be in the desired range. In short, h-BAs possess every quality that is crucial for an anode material and thus it is interesting to see h-BAs in alkali-based battery technologies.     

Cobaltocene as a spin filter

In the context of investigating organic molecules for molecular electronics, doping molecular wires with transition metal atoms provides additional means of controlling their transport behavior. The incorporation of transition metal atoms may generate spin dependence because the conduction channels of only one spin component align with the chemical potential of the leads, resulting in a spin polarized electric current. The possibility to create such a spin polarized current is investigated here with the organometallic moiety cobaltocene. According to our calculations, cobaltocene contacted with gold electrodes acts as a robust spin filter: Applying a voltage less than 0.2 V causes the current of one spin component crossing the molecular bridge to be two orders of magnitude larger than the other. We address the key issue of sensitivity to molecule-lead geometry by showing that a weak barrier generated by CH(2) groups between the cobaltocene and the leads is crucial in reducing the sensitivity to the contact geometry while only reducing the current modestly. These results suggest cobaltocene as a robust basic building block for molecular spintronics.     

Density functional crystal vs. cluster models as applied to zeolites

In order to compare solid and cluster models of zeolites, we have studied the substitution Si⁴⁺→Al³⁺+H⁺ on the T₁ site of mordenite in the dilute limit using a self-consistent, full potential, local density functional (LDF) approach. Clusters size ranged from 9 to 105 atoms. Two crystal models with different Al concentrations were used. The first contained one substitution site per primitive cell of 72 atoms, the other one per conventional cell, containing 144 atoms. The unrelaxed substitution energies as computed with cluster and crystal models correspond well if the cluster results are extrapolated to infinite radius. Size effects are much smaller in crystal models. In addition, a structure relaxation (with fixed unit cell) was carried out for pure-silica offretite, a zeolite with 54 atoms per unit cell, and pure-silica mordenite, with 144 atoms per unit cell, starting from the low aluminum content X-ray crystallographic structure. In the offretite and mordenite optimizations full use was made of the D_3h¹–P $ \bar 6 $m2 and the nonsymmorphic D_2h¹⁷–Cmcm space group symmetry, respectively. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 68: 135–144, 1998     

Insight into the short-range structure of amorphous iron inositol hexaphosphate as provided by (31)P NMR and Fe X-ray absorption spectroscopy

Short-range structure and formation of amorphous aggregates of iron inositol hexaphosphate (iron phytate) were studied by broadline solid-state 31P NMR and Fe X-ray absorption spectroscopy. It was shown that bonds P-O-Fe with strong covalent character exist in solid substances. Iron in these substances is octahedrally coordinated by six oxygen atoms and further monodentatly bonded to three or four phosphorus atoms. In this way, iron generates -P-O-Fe-O-P- intermolecular connections. An insight into the formation of the network was obtained by studying structural changes in iron phytates with increasing concentrations of iron. It was shown that the solid network builds when at least four out of six phosphate groups per one phytic molecule bond to iron atoms and thus participate in the intermolecular connections. This leads to iron phytate with approximately two iron atoms per one molecule of phytate. When the concentration of iron in aggregates increases, the number of P-O-Fe bonds, and thus the number of phosphate groups that are bonded to iron, increases. Solid iron phytate with approximately four iron atoms per one molecule of phytate is almost saturated with iron. Its short-range structural properties can be explained well by a structure that is approaching an idealized model, in which each phosphate group is bonded to two iron atoms and each iron atom is bonded to three phosphorus atoms and is shared between two phytic molecules.     

Cd(Ⅱ)双苯吡唑基吡啶-草酸混配合物的合成、结构与性质

合成了Cd(Ⅱ)与类蝎型吡唑衍生物和草酸的混合配体的配合物[Cd2(HL)2(ox)]·1.5H2O(H2L=2,6-二(5-苯基-吡唑-3-基)吡啶,H2ox=草酸)。 通过元素分析、红外光谱、紫外光谱、X射线粉末衍射(PXRD)和X射线单晶结构分析确定了配合物的结构。 配合物晶体属于三斜晶系、P-1空间群,Cd(Ⅱ)是六配位,由一个ox2-基中的2个O原子和来自2个HL-中的4个N原子配位,构成变形八面体配位构型,而相邻Cd(Ⅱ)原子间均通过HL-上的N原子和草酸根分别连接形成2条互不相交的一维无限链状结构。 性质测试结果表明,该配合物具有良好的热稳定性和荧光特性,对环己烷氧化反应也具有一定的催化活性。     

Gravitational smoothing as a global optimization strategy

An optimization scheme for atomic cluster structures, based on exaggerating the importance of the gravitational force, is introduced. Results are presented for calculations on Lennard-Jones clusters of 13, 38, and 55 atoms, and the 13-atom Morse cluster.     

The First Complex of Benzilbis(thiosemicarbazone) acting as Bridging Ligand only through the Sulfur Atom

The first complex with benzilbis(thiosemicarbazone) LH₆ acting only as a bridge between two metallic centres through the sulfur atoms, was obtained from the reaction with methylmercury chloride. This complex shows a 1:2 ligand : mercury ratio and has been spectroscopically characterized and recrystallized in toluene. The ligand acts as a dianion, with an intermediate situation between cis and trans dispositions, and it is bonded to both methylmercury moieties through the sulfur atoms, giving a binuclear complex with linear CS coordination for the mercury atoms.