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.

Cation−Anion Interactions and Polar Structures in the Solid State

Abstract: Complicated structures where oxygen and fluorine are found together in one framework, where deviations from Pauling's second crystal rule (PSCR) are expected, often result in structures with important physical properties. The [NbOF5]2- anion and therefore all the individual Nb-O and Nb-F bonds are ordered in noncentrosymmetric KNaNbOF5 and centrosymmetric CsNaNbOF5. The Na/K- and Na/Cs-O/F interactions in these phases, in particular the expected deviations from PSCR and the bond valence model, reveal the essential role of the small potassium cations in the acentric packing of the [NbOF5]2- anion. KNaNbOF5 crystallizes in the orthorhombic and polar space group Pna21 (No. 33) with lattice constants a = 11.8653(11) A, b = 5.8826(6) A, c = 8.1258(8) A, and Z = 4, while CsNaNbOF5 crystallizes in the orthorhombic space group Pbcn (No. 60) with lattice constants a = 8.3155(7), b = 13.3176(11), c = 11.1314(9), and Z = 8.

X-ray absorption study of Ti-activated sodium aluminum hydride

Abstract: Ti K-edge x-ray absorption near edge spectroscopy (XANES) was used to explore the Ti valence and coordination in Ti-activated sodium alanate. An empirical relationship was established between the Ti valence and the Ti K-edge onset based on a set of standards. This relationship was used to estimate oxidation states of the titanium catalyst in 2 mol% and 4 mol% Ti-doped NaAlH4. These results demonstrate that the formal titanium valence is zero in doped sodium alanate and nearly invariant during hydrogen cycling. A qualitative comparison of the edge fine structure suggests that the Ti is present on the surface in the form of amorphous TiAl3.

Chemistry and applications of oxynitride perovskites

Abstract: Oxynitride perovskites of early transition metals and rare earth or alkaline earth elements have been reported in the last decade as non-toxic pigments, colossal magnetoresistive materials, high permittivity dielectrics and photocatalysts. Nitride and oxide may occupy the same sites in the perovskite structure, forming solid solutions with ratios that are adjusted by synthesis. The valence states of cations, the bond covalency and the energy of the electronic states can be tuned by the introduction of nitrogen as a consequence of its lower electronegativity, higher electronic polarisability and higher formal anion charge relative to oxygen. This feature article will discuss the influence of the above factors on the crystal chemistry and properties of this group of materials that have emerged as a result of the development of new and controlled synthetic methodologies.

Determining Relative f and d Orbital Contributions to M–Cl Covalency in MCl62– (M = Ti, Zr, Hf, U) and UOCl5– Using Cl K-Edge X-ray Absorption Spectroscopy and Time-Dependent Density Functional Theory

Abstract: Chlorine K-edge X-ray absorption spectroscopy (XAS) and ground-state and time-dependent hybrid density functional theory (DFT) were used to probe the electronic structures of Oh-MCl62– (M = Ti, Zr, Hf, U) and C4v-UOCl5–, and to determine the relative contributions of valence 3d, 4d, 5d, 6d, and 5f orbitals in M–Cl bonding. Spectral interpretations were guided by time-dependent DFT calculated transition energies and oscillator strengths, which agree well with the experimental XAS spectra. The data provide new spectroscopic evidence for the involvement of both 5f and 6d orbitals in actinide–ligand bonding in UCl62–. For the MCl62–, where transitions into d orbitals of t2g symmetry are spectroscopically resolved for all four complexes, the experimentally determined Cl 3p character per M–Cl bond increases from 8.3(4)% (TiCl62–) to 10.3(5)% (ZrCl62–), 12(1)% (HfCl62–), and 18(1)% (UCl62–). Chlorine K-edge XAS spectra of UOCl5– provide additional insights into the transition assignments by lowering the symmetry...

XPS Valence Characterization of Lithium Salts as a Tool to Study Electrode/Electrolyte Interfaces of Li-Ion Batteries

Abstract: X-ray photoelectron valence spectra of lithium salts LiBF4, LiPF6, LiTFSI, and LiBETI have been recorded and analyzed by means of density functional theory (DFT) calculations, with good agreement between experimental and calculated spectra. The results of this study are used to characterize electrode/electrolyte interfaces of graphite negative electrodes in Li-ion batteries using organic carbonate electrolytes containing LiTFSI or LiBETI salts. By a combined X-ray photoelectron spectroscopy (XPS) core peaks/valence analysis, we identify the main constituents of the interface. Differences in the surface layers' composition can be evidenced, depending on whether LiTFSI or LiBETI is used as the lithium salt.