M. Grodzicki

Electronegativity and the concept of charge capacity

Abstract A general discussion of electronegativity and electronegativity equalization is presented as background for the concept of charge capacity; the latter is the ability of an atom to absorb or yield electronic charge. We have discussed charge capacity in relation to a variety of atomic and molecular properties, e.g. atomic polarizabilities and outer shell properties, electron affinities, dipole moments, electronic density distributions, dissociation energies, electrostatic potentials, spectroscopic measurements, acidities, etc. Significant increases in charge capacity and decreases in electronegativity in going from the first to subsequent rows of the periodic table are important in explaining (especially for columns IV–VII) the discontinuities in many physical and chemical properties that occur between these rows. It is demonstrated that both intrinsic electronegativities and charge capacities must be considered in order to understand the redistribution that occurs when atoms interact to form molecules. We discuss many seemingly anomalous observations of chemical behavior that are explained quite readily when both of these factors are taken into account.

Photoelectron spectra of group V compounds. The elements: Sb4

Abstract The high-temperature He I photoelectron (PE) spectrum of gaseous Sb 4 is presented and assigned on the basis of the known PE ionisation energies of As 4 and P 4 and from SCC Xa eigenvalues and eigenvectors. Implications for the PE spectra of related antimony compounds are discussed.

What kind of support for the interpretation of infrared spectra can be expected from cluster MO calculations on zeolite systems?: Application of the SCC-Xα method to the sorption complex of carbon monoxide on a S1 calcium ion in zeolite A

Abstract In order to get more detailed information on the adsorbed state of carbon monoxide in zeolites A, quantum chemical SCC-Xα calculations have been performed on a M[Si3Al3O6(OH)12] cluster (M  Ca2+, Na+), modelling the favoured sorption site in front of S1 cations. Evaluation of the electronic structure gave several well-separated energy bands. CO bonding to the cluster is predicted for linear MCO as well as MOC arrangements. From the total electronic energies an equilibrium distance CaC of 2.7 A can be inferred. Both findings are in agreement with results from classical calculations of the interaction of CO with zeolite Na4Ca4A and are able to explain the observed IR band pattern. Ascribing the partial charges from Xα calculations to the atoms of the cluster in the classical model leads to improvement of the electric field strength values inside the zeolite skeleton from which frequency shifts more consistent with the observed spectrum are expected.

Theoretical investigation of adsorption of water dimers on a Ni(110) surface

Abstract SCC-Xα molecular orbital calculations are performed on a water dimer adsorbed on a Ni(110) surface in order to explain a recent angle resolved photoelectron spectrum of this system. Minimizing the total energy as a function of the position of the bridging hydrogen, an increased O D -H br D distance of 1.31 A is found within the donator part of the dimer. On the basis of this geometry, the experimental photoelectron spectrum is fairly well reproduced while this cannot be achieved with the gas phase dimer geometry. Moreover, the calculations indicate that the observed dissociation of water on this surface could take place via the chemical reaction (H 2 O) 2 → HO ⋯ H··OH 2 .

Molecular orbital calculations and normal coordinate analysis of CO2 and N2O in zeolites

Abstract SCC-Xα MO calculations and normal coordinate analysis were performed on CO 2 and N 2 O in the free and adsorbed state. For approaching S-I cations a linear arrangement with the molecular axis perpendicular to the plane of the oxygen six-ring is confirmed. Electronic charge density is withdrawn from the antibonding HOMO of the adsorbed molecules towards the zeolite cluster, connected with an internal charge redistribution within the molecule. The changes of the respective force elements are consistent with the quantum chemical results. The results assist the assignment of the IR bands of the sorption complexes, proving the formation of both O-bound and N-bound species in case of N 2 O, the latter being energetically more favourable.

Application of semiempirical MO calculations to the interaction of hydrocarbons with zeolites

Abstract In order to support previous spectral studies and normal coordinate analysis data, the semiempirical SCC-Xα method has been applied to the interaction of propene and cyclopropane with Ca 2+ ions in front of the sixford windows connecting the sodalite units and the supercages in faujasites and A-type zeolites. From preliminary results, the ion can be approached by propene in a geometry intermediate between parallel or perpendicular orientation of its molecular plane normal to the double bond, while in case of cyclopropane an edge-on interaction seems to be favoured.

Bonding modes in the analogous and isoelectronic group VB/VA compounds As(O)Cl3 and Nb(O)Cl3. An ultraviolet photoelectron-spectroscopic and SCC-Xα study

The He Iα photoelectron spectra of gaseous ‘non-existent’ As(O)Cl3 and of Nb(O)Cl3 have been compared and assigned using the SCC-Xα method. In order to confirm the interpretation, correlations with the known ionization potentials of isomorphous P(O)Cl3 and V(O)Cl3, respectively, are considered. Differences in bonding modes are discussed and illustrated with respect to the SCC-Xα population analyses, to the relative central atomic orbital contributions, to the atomic energy levels and to the experimental ionization energies of the parent AsCl3 and PCl3.

Profitability of the combined application of Mo calculations and vibrational analysis on intrazeolitic sorption complexes

Abstract The adsorption of CO in Ca- and Ni-exchanged zeolite A is studied by IR-spectroscopy, quantum chemical calculations and vibrational analysis. A similar experimental frequency shift of the CO fundamental vibration is shown to arise from different mechanisms. In case of Ca-bonded CO the main contribution comes from direct strengthening of the CO bond while in case of Ni-bonded CO vibrational coupling turns out to be the dominant mechanism.

Measured Electron Density Distributions in Crystals as a Basis for Band Structure Calculations

General methods are outlined for constructing Fourier coefficients of the Coulomb and Slater potentials in crystals from X-ray diffraction measurements of the charge density supplemented with atomic Hartree-Fock data. Corrections for temperature effects are discussed. Asymptotic expressions for the Fourier coefficients are also given, as well as an expression for the Coulomb contribution to the binding energy.

Self-Consistent-Charge Xα Calculations on Sorption Complexes of Nitrous Oxide Attached To Transition Metal Occupied Zeolite Clusters

Abstract Quantum chemical SCC-Xα MO calculations were carried out on an aluminosilicate six-ring cluster occupied by nickel or copper ions, approached by a nitrous oxide molecule in N- or O-faced interaction in order to facilitate the assignment of infrared bands. In all cases stable sorption complexes are found with stronger bonding in the case of nickel and the M n+ -NNO species. Electronic structure and charge distribution are analyzed, revealing an N-N to N-O bond charge redistribution for both orientations on nickel, while a loss of electronic charge for the copper species results. The splitting of the v 1 and the frequency shift of the v 3 fundamental band of N 2 O on nickel ion-exchanged zeolite A may be explained by the different overlap populations of the bonds.