Extended Huckel Type Research Articles

Combining Chirality and Hydrogen Bonding in Methylated Ethylenedithio-Tetrathiafulvalene Primary Diamide Precursors and Radical Cation Salts

Methyl-and dimethyl-ethylenedithio-tetrathiafulvalene ortho-diamide donors Me-EDT-TTF(CONH2)2 (1a) and DM-EDT-TTF(CONH2)2 (1b) have been prepared by the direct reaction of the corresponding diester precursors with aqueous ammonia solutions. The neutral (rac)-1a, (S)-1a and (S,S)-1b donors have been characterized by single crystal X-ray diffraction. In the three compounds, which crystallized in the non-centrosymmetric monoclinic space-group P21, the amide groups are disordered, yet they form the classical intramolecular hydrogen bond for such ortho-diamide motif. Electrocrystallization experiments afforded the mixed valence radical cation salts [(S,S)-1b]2XO4 and [(R,R)-1b]2XO4 (X = Cl, Re) containing four independent donors in the asymmetric unit, with the positive charge localized essentially on two donors while the two others are neutral. The topology of the organic layer is of '-type. Single crystal resistivity measurements show semiconducting behavior for [(S,S)-1b]2ClO4 and [(R,R)-1b]2ReO4, with a room temperature conductivity of 5 10-5 S cm-1 and activation energies Ea ≈ 3000 K. Tight-binding band structure calculations of extended Huckel type in combination with DFT calculations are in agreement with the semiconducting behavior and suggest a localized Mott type semiconductor rather than a band gap semiconductor.

ChemInform Abstract: Prediction of Activity Coefficients for Uni‐Univalent Electrolytes in Pure Aqueous Solution

AbstractReview: 53 refs.

Prediction of Activity Coefficients for Uni‐univalent Electrolytes in Pure Aqueous Solution

AbstractParameter‐free activity coefficient equations were tested in addition to those containing one, two, three or four electrolyte‐dependent parameters with the experimental activity coefficients obtained from the literature data for aqueous solutions of the following electrolytes at 298.15 K: KCl, NaCl, RbCl, KBr, RbBr, CsBr, KI, RbI, KNO3, and KH2PO4. The experimental activity coefficients of each electrolyte considered can be reproduced within the uncertainty of the measurements up to the molality of the saturated solution by using a three‐parameter equation of the extended Hückel type. The best Hückel equations are given for all electrolytes in question. The results from the present studies reveal that the parameter‐free equations can be reliably used in thermodynamic studies only for very dilute electrolyte solutions. On the other hand, in most cases, a good agreement with the experimental data is obtained with the one‐parameter equations of Bromley [14] and Kusik and Meissner [13], with the two‐parameter equation of Bretti et al. [15], and with the three‐ or four‐parameter equation of Hamer and Wu [19] in addition to the three‐parameter Pitzer equation [23], with almost all parameter values suggested in the literature. In several cases, these equations seem to apply to much higher molalities than those used in the parameter estimations. Therefore, the best of these equations may have important applications in calculations associated with the dissolution and crystallization processes of these salts.

The FAKE method of molecular orbital calculation

The FAKE method of semiempirical molecular orbital calculation is described and illustrated for representative compounds of H, C, N, O, and F. The method is of extended Huckel type, but it includes neighbor charge effects and uses exactly calculated kinetic energy contributions.

Color and Conductivity in Cu2O and CuAlO2: A Theoretical Analysis of d10···d10 Interactions in Solid-State Compounds

The influence of homoatomic d10···d10 interactions in the structural and physical properties of some copper-containing oxides has been investigated by using semiempirical band structure calculations of the extended Huckel type. Comparison of the band structures of CuAlO2 and Cu2O, two compounds with Cu(I) ions in practically identical coordination environments, reveals that the spatial arrangement of Cu···Cu contacts is responsible for their markedly different electrical and optical properties. The three-dimensional net of short Cu···Cu distances present in Cu2O is found to be essential for the appearance of color in this p-type semiconductor. In doped CuAlO2, on the contrary, the 2-D nature of the array of Cu···Cu contacts leads to optical transparency and a lower conductivity if compared to cuprite.

Metallkomplexe mit funktionalisierten Schwefelliganden. XIV. Synthese von Thiosulfinatokomplexen über die Oxidative Addition von Platin(0)-Komplexen an 2,3,4-Benzotrithiepin-1-oxid

The platinum(0) compounds L2Pt(η2-C2H4) [L = PPh3, 1/2 dppf, 1/2 (R,R)-(–)-DIOP] 3a–c react with the 2,3,4-benzotrithiepin 1-oxides 2a–c to give the platinum(II) thio-lato thiosulfinato complexes L2Pt[S–S(O)–CH2–C6R12R22-CH2–S] (R1 = H, R2 = CH3; R1 = CH3, R2 = H) 4a–6c. Treatment of 5a with an excess of PBu3 efficiently affords (Bu3P)2Pt[S–S(O)–CH2–C6Me2H2–CH2–S] 7 by substitution of PPh3. Complex 7 reacts in solution with PBu3 to the platinum(II) sulfenato thiolato complex (Bu3P)2Pt[S(O)–CH2–C6Me2H2–CH2–S] 8 as well as S=PBu3. The compounds 4a–6c have been characterized by analytical and spectroscopic methods. Simple qualitative MO calculations of the extended Huckel type by using the CACAO package indicate that the platinum(0) species acts as a Lewis acid attacking the nucleophilic sulfur atom S(3).

Rhenium-(III) and -(V) hydride complexes with modified poly(pyrazolyl)borates

The hydrides [ReH2{κ3-(OR)(µ-OR)B(pz)2}(PPh3)2] (R = Me 1 or Et 2) and [ReH4{κ3-(H)(µ-OR)B(3,5-Me2pz)2}(PPh3)] (R = Me 3 or Et 4) have been obtained by treating [ReOCl3(PPh3)2] with Na[H2B(pz)2] or Na[H2B(3,5-Me2pz)2] in alcohols (ROH, R = Me or Et) at room temperature. The same type of reaction with Na[Ph2B(pz)2], using methanol as solvent, gave [ReO(OMe){κ2-Ph2B(OMe)(pz)}2] 5, although in a very low yield. The characterization of the new compounds involved IR and 1H NMR spectroscopies, 31P-{1H} NMR, variable temperature 1H and 31P NMR studies, T1 and JH-D measurements. The crystal structures of the complexes 1, 4 and 5 were also determined. The structural parameters of the hydride ligands in 1 and 4 have not been obtained, but were tentatively assigned by X-ray diffraction associated with molecular orbital calculations of ab initio and extended Huckel type.

Synthesis, molecular and electronic structure of Ru3 isomeric clusters carrying C8 rings bonded in allenylic and acetylenic modes

The two new cluster complexes [Ru 3 H 2 (CO) 9 (C 8 H 10 )] 1 and [Ru 3 H(CO) 9 (C 8 H 11 )] 2 have been isolated as the products of thermolysis of [Ru 3 (CO) 12 ] in octane containing cycloocta-1,3-diene. The two species are structural isomers ideally differing only in the transfer of one hydrogen atom from the organic ligand to the metal core. The organic ligand in 2 is bonded in an allenyl µ 3 -η 3 fashion, the first allenylic bonded ring system to have been reported, whereas in 1 the ligand is, more conventionally, bound in µ 3 -η 2 fashion with the second unsaturated CC bond not involved in bonding to the cluster. The solid-state structures of 1 and 2 have been studied by single-crystal X-ray diffraction. The bonding of the organic ligands in the clusters has been investigated by molecular orbital calculations of the extended-Huckel type.

Molecular Orbital Model of Electron Delocalization in Mixed-Valence Trimeric Clusters

A simple extended Huckel type molecular orbital model is used to study electronic distributions in mixed-valence iron−oxygen clusters containing three octahedral subunits. Two different structures were considered: one-atom bridged octahedra and octahedra with common faces. The stability of symmetric structures relative to different non-totally symmetric distortions leading to the vibronic charge trapping was examined. It appears that the distribution of the excess electron cannot be described by the simple alternative “localization−delocalization”. The type of electronic distribution depends on the arrangement of octahedral units, the metal−metal distances, and the electronic configurations. The molecular orbital approach gives some insights into the peculiarities of the intramolecular electron delocalization in mixed-valence iron−oxygen trimers which are important for their catalytic activity.

Effect of structural modulation on the electronic structure of Bi-based superconductors

Tight-binding band calculations of the extended Huckel type were performed on the Cu 4Bi 4O 16 12− complex modelling the Bi 2Sr 2CuO 6 sublattice. We investigate the effect of structural modulation on the electronic energy spectrum and chemical bonding nature of individual atoms. The results show that the structural modulation causes a splitting of the Bi 6 p states and a shift of the Bi 6 p-block bands toward the lower energy region, accompanied by a charge modulation of Bi and O atoms along the Bi-O double layers.

Theoretical study of chemisorption of acetylene on the Cu(100) surface

The chemisorption of acetylene on the Cu(100) surface has been studied by molecular orbital calculations of the extended Huckel type. Separating the adsorbate–surface interaction into different components, it was found that the overlaps of the π orbitals of acetylene with the s and pz orbitals of copper at the surface are the main sources of this interaction. Electron transfer from metal to adsorbate leads to significant weakening of the C—C bond. However, it is the covalent interaction which accounts for most of the adsorbate–surface stabilization.

Mechanism of the antipodal effect with borane cages

With the EB11H11(1) and EB9H9(2) series, CNDO/2 and extended Huckel type calculations show that with decreasing electron density on the vertex E: AIR2– > BH2– > CH– > NH > S the electron density on the antipodal skeletal atom decreases proportionally in the tangential px and py(π) atomic orbitals and increases in the radial pz orbital through both series; this explains contradictory information about the electron density on the antipodal atom, a low electron density being indicated by the 11B NMR chemical shift and a high one being deduced from chemical behaviour.

Modeling of chemical interactions at Cr/Cu interfaces

Band calculations of the Extended Huckel type were performed to investigate the nature of chromium-copper interfaces. Model systems were comprised of a chromium or copper atom in close proximity to a three- or four-layered slab of substrate material. The substrates considered were metallic chromium, metallic copper, Cr 2O 3, and Cu 2O. Preferred geometries of attack were inferred from the total energy and projected Density of States analyses. Based on the total energy, metal-metal bonds were found to form preferentially.

Acid-base properties of copper oxides and fluorides by means of band calculations: Relevance to metal-polymer adhesion

Classification of acids and bases in the Lewis sense implies electronic participation and it is extendable to non-protonic solvent interactions as well as solventless reactions. In many microelectronic applications, interfacial interactions between a polymer and a metal occur and contribute to the resulting adhesion of the bond. In the practical sense, metal surfaces are either oxidized or can be chemically altered by process conditions; therefore, the interaction is through a modified surface. The present study shows how tight binding calculations of the extended Huckel type can be used to estimate the relative acid strengths of copper, its oxides and fluorides. The trends obtained from bulk and surface layers in each case were related to the Fermi level of the crystal and the number of empty states derived from the copper 3d orbitals. Our results show the relative acid strengths follow the trend: CuF2 > CuO > CuF ~ Cu2O > Cu The methods used here can be directly applicable to classify the relative acid ...

A new one-electron model for extended H�ckel type molecular orbital calculations

A new form of Coulomb and resonance integrals for extended Huckel type molecular orbital calculations was derived. In this model an electron moving in a molecule, when it stays in the neighborhood of the center of an atom in the molecule, sees the potential of the corresponding isolated atom. Compared with the well-known forms of Coulomb and resonance integrals, each integral derived from this model considers the influences from all atoms in the molecule, and includes the concept of atomic cell. The similarities of this model to other extended Huckel type formulations are also examined.

Fake molecular-orbital calculations

The FAKE method of approximate molecular-orbital calculations is presented and illustrated by application to a number of molecules. The method is of the extended Huckel type but uses accurately computed kinetic-energy matrix elements and avoids scale factors of the Wolfsberg—Helmholtz type. It also includes neighbor-atom charge effects and single-center off-diagonal matrix elements. These features permit FAKE occupied-orbital energies and charge distributions to come into close agreement with corresponding ab initio quantities.

Vacuum ultraviolet spectra of osmium tetroxide and ruthenium tetroxide

The gas phase absorption spectra of the compounds OsO4 and RuO4 were measured between 2500 and 1050 Å with a Baird 1−m vacuum monochrometer of 1.0 Å bandwidth. Both tetroxides show many electronic absorption bands in this region with diffuse vibrational structure. No spectra of OsO4 or RuO4 have been previously reported below 2200 Å. Absorption maxima for OsO4, which were not previously reported, occur at 48 140, 63 620, 73 960, 85 620, 86 920, 89 160, 90 800, and 91 940 cm−1. The spectrum of RuO4 showed band maxima at 50 660, 64 620, 72 700, 76 420, 79 040, 83 100, 88 860, and 92 080 cm−1. The general appearance and relative strengths of various absorption bands in the spectra of these molecules were similar, with the energy of apparently corresponding transitions shifted to the red in RuO4 by approximately 10 000 cm−1. Most of the strong electronic transitions have been tentatively assigned on the basis of extended Hückel type calculations. The results of these calculations correlated reasonably well with the spectral data obtained. Bands are present in the spectra of both molecules which may be the first members of Rydberg series.

Rotation-independent conjugation between a sulphur(IV)-nitrogen double bond and a sulphonyl group

Extended Huckel type calculations suggest that the bond populations in SS-dimethyl-N-methyl-sulphonylsulphimide (Me2S:N·SO2Me) are independent of the dihedral angle of the N–SVI bond rotation; the barriers of the rotation can be correlated to steric and lone pair effects. A theoretical interpretation of the experimentally observed interconversion of chiral conformers is given.

Substituent effects on the rotational strength of the n–π* carbonyl band

The quantitative contribution of a substituent in the α-axial position of a cyclohexanone derivative to the rotatory strength of the 3000 An–π* carbonyl band is discussed. Calculations of the extended Huckel type on a model compound indicated the importance of delocalisation through the σ framework and predict variation of rotatory strength with electronegativity and overlap. Observed values of substituent contributions are discussed in terms of these predictions.