Valence (chemistry)

About: Valence (chemistry) is a research topic. Over the lifetime, 24937 publications have been published within this topic receiving 645252 citations. The topic is also known as: valency.

Electron pairing and chemical bonds. Chemical structure, valences and structural similarities from the analysis of the Fermi holes

Abstract: A new method of visualisation of bonding in molecules is introduced. The method is based on the analysis of Fermi holes associated with conditional probabilities of finding one electron of the pair provided the second, reference, electron is localised in a certain molecular region. Based on this analysis it is possible to get a clear and highly visual insight into the structure of molecular fragments (functional groups) in molecules. In addition to this visualisation, the new approach opens the possibility of the new definition of atomic and group valence and, also, can be applied as a new means of the quantitative characterisation of similarity of structural fragments in the series of related molecules.

Electronic and structural properties of GaN by the full-potential linear muffin-tin orbitals method: The role of the d electrons.

Abstract: The structural and electronic properties of cubic GaN are studied within the local-density approximation by the full-potential linear muffin-tin orbitals method. The Ga 3d electrons are treated as band states, and no shape approximation is made to the potential and charge density. The influence of d electrons on the band structure, charge density, and bonding properties is analyzed. Due to the energy resonance of Ga 3d states with nitrogen 2s states, the cation d bands are not inert, and features unusual for a III-V compound are found in the lower part of the valence band and in the valence charge density and density of states. To clarify the influence of the d states on the cohesive properties, additional full- and frozen-overlapped-core calculations were performed for GaN, cubic ZnS, GaAs, and Si. The results show, in addition to the known importance of core-valence exchange-correlation nonlinearity, that an explicit description of closed-shell interaction has a noticeable effect on the cohesive properties of GaN. Since its band structure and cohesive properties are sensitive to a proper treatment of the cation d bands, GaN appears to be somewhat exceptional among the III-V compounds and reminiscent of II-VI materials.

N doping of TiO2(110): photoemission and density-functional studies.

Abstract: The electronic properties of N-doped rutile TiO2(110) have been investigated using synchrotron-based photoemission and density-functional calculations. The doping via N2+ ion bombardment leads to the implantation of N atoms (approximately 5% saturation concentration) that coexist with O vacancies. Ti 2p core level spectra show the formation of Ti3+ and a second partially reduced Ti species with oxidation states between +4 and +3. The valence region of the TiO(2-x)N(y)(110) systems exhibits a broad peak for Ti3+ near the Fermi level and N-induced features above the O 2p valence band that shift the edge up by approximately 0.5 eV. The magnitude of this shift is consistent with the "redshift" observed in the ultraviolet spectrum of N-doped TiO2. The experimental and theoretical results show the existence of attractive interactions between the dopant and O vacancies. First, the presence of N embedded in the surface layer reduces the formation energy of O vacancies. Second, the existence of O vacancies stabilizes the N impurities with respect to N2(g) formation. When oxygen vacancies and N impurities are together there is an electron transfer from the higher energy 3d band of Ti3+ to the lower energy 2p band of the N(2-) impurities.

Electronic structure of α-alumina and its defect states

Abstract: We have investigated the electronic structure of $\ensuremath{\alpha}$-alumina and its defect states by using a semiempirical method. Our results show that the fundamental gap is indirect, and the charge transfer enhances the hybridization of aluminum and oxygen orbitals, which in turn leads to the broad upper and lower valence bands. Using the calculated total and orbital density of states, we have provided a consistent interpretation of the existing spectra. For the ideal $\ensuremath{\alpha}$-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$(0001) surface we have found that the Al---O bonds at the surface have a considerable covalent character and the Al---dangling bonds produce the major surface-state band. Energy positions of the oxygen-vacancy states, and of the surface states, strongly suggest that the oxygen deficiency is responsible for some of the lowenergy structures in the excitation spectra.

X-ray emission spectroscopy to study ligand valence orbitals in Mn coordination complexes

Abstract: We discuss a spectroscopic method to determine the character of chemical bonding and for the identification of metal ligands in coordination and bioinorganic chemistry. It is based on the analysis of satellite lines in X-ray emission spectra that arise from transitions between valence orbitals and the metal ion 1s level (valence-to-core XES). The spectra, in connection with calculations based on density functional theory (DFT), provide information that is complementary to other spectroscopic techniques, in particular X-ray absorption (XANES and EXAFS). The spectral shape is sensitive to protonation of ligands and allows ligands, which differ only slightly in atomic number (e.g., C, N, O...), to be distinguished. A theoretical discussion of the main spectral features is presented in terms of molecular orbitals for a series of Mn model systems: [Mn(H2O)6]2+, [Mn(H2O)5OH]+, [Mn(H2O)5NH2]+, and [Mn(H2O)5NH3]2+. An application of the method, with comparison between theory and experiment, is presented for the solvated Mn2+ ion in water and three Mn coordination complexes, namely [LMn(acac)N3]BPh4, [LMn(B2O3Ph2)(ClO4)], and [LMn(acac)N]BPh4, where L represents 1,4,7-trimethyl-1,4,7-triazacyclononane, acac stands for the 2,4-pentanedionate anion, and B2O3Ph2 represents the 1,3-diphenyl-1,3-dibora-2-oxapropane-1,3-diolato dianion.