scholarly journals Correlations between individual bond-valence parametersr0and stereochemistry of cations with lone-pair electrons

1996 ◽  
Vol 52 (a1) ◽  
pp. C309-C309 ◽  
Author(s):  
X. Wang ◽  
F. Liebau
Keyword(s):  
Lone Pair ◽  
Bond Valence ◽  
Individual Bond ◽  
Lone Pair Electrons

Critical Survey of the method of ionic-homopolar resonance

1951 ◽  
Vol 207 (1088) ◽  
pp. 63-73 ◽  
Keyword(s):  
Dipole Moment ◽  
Lone Pair ◽  
Atomic Radius ◽  
Substantial Part ◽  
Critical Survey ◽  
Conventional Theory ◽  
Total Dipole Moment ◽  
Atomic Orbitals ◽  
Individual Bond ◽  
Lone Pair Electrons

Some of the theoretical difficulties in the method of ionic-covalent resonance are discussed. They include our ignorance of the fundamental energies, and also of the orbitals used. If these are hybrids, as usually occurs, considerable care is required in using the conventional theory because: (1) the atomic radius, and (2) the effective electronegativity of a hybrid depend on the degree of mixing of the basic atomic orbitals. In polyatomic molecules the lone-pair electrons play a substantial part in determining the total dipole moment, and there are further difficulties associated with (1) independence, (2) partial delocalization, and (3) possible 'bent’ character of the bonds. As a result many bonds (e.g. CH, NH, OH) are intrinsically much less ionic than is usually supposed. In addition the dipole moment of a molecule does not depend in any simple way upon the formal charges associated with the atoms; nor does it provide a completely satisfactory basis for assigning individual bond moments. The paper concludes with an outline of some possible improvements which merit further research.

Influence of lone-pair electrons of cations on bond-valence parameters

1996 ◽  
Vol 211 (7) ◽  
Author(s):  
X. Wang ◽  
F. Liebau
Keyword(s):  
Lone Pair ◽  
Bond Valence ◽  
Lone Pair Electrons

AbstractAccording to the current bond-valence concept, the valence

scholarly journals Bond-length distributions for ions bonded to oxygen: results for the non-metals and discussion of lone-pair stereoactivity and the polymerization of PO4

2018 ◽  
Vol 74 (1) ◽  
pp. 79-96 ◽  
Author(s):  
Olivier Charles Gagné ◽  
Frank Christopher Hawthorne
Keyword(s):  
Metal Ions ◽  
Bond Length ◽  
Oxidation State ◽  
Lone Pair ◽  
Bond Valence ◽  
Group 14 ◽  
Coordination Polyhedra ◽  
Bond Lengths ◽  
Secondary Bonds ◽  
Lone Pair Electrons

Bond-length distributions are examined for three configurations of the H+ ion, 16 configurations of the group 14–16 non-metal ions and seven configurations of the group 17 ions bonded to oxygen, for 223 coordination polyhedra and 452 bond distances for the H+ ion, 5957 coordination polyhedra and 22 784 bond distances for the group 14–16 non-metal ions, and 248 coordination polyhedra and 1394 bond distances for the group 17 non-metal ions. H...O and O—H + H...O distances correlate with O...O distance (R 2 = 0.94 and 0.96): H...O = 1.273 × O...O – 1.717 Å; O—H + H...O = 1.068 × O...O – 0.170 Å. These equations may be used to locate the hydrogen atom more accurately in a structure refined by X-ray diffraction. For non-metal elements that occur with lone-pair electrons, the most observed state between the n versus n+2 oxidation state is that of highest oxidation state for period 3 cations, and lowest oxidation state for period 4 and 5 cations when bonded to O2−. Observed O—X—O bond angles indicate that the period 3 non-metal ions P3+, S4+, Cl3+ and Cl5+ are lone-pair seteroactive when bonded to O2−, even though they do not form secondary bonds. There is no strong correlation between the degree of lone-pair stereoactivity and coordination number when including secondary bonds. There is no correlation between lone-pair stereoactivity and bond-valence sum at the central cation. In synthetic compounds, PO4 polymerizes via one or two bridging oxygen atoms, but not by three. Partitioning our PO4 dataset shows that multi-modality in the distribution of bond lengths is caused by the different bond-valence constraints that arise for Obr = 0, 1 and 2. For strongly bonded cations, i.e. oxyanions, the most probable cause of mean bond length variation is the effect of structure type, i.e. stress induced by the inability of a structure to follow its a priori bond lengths. For ions with stereoactive lone-pair electrons, the most probable cause of variation is bond-length distortion.

Effect of delocalization of nonbonding electron density on the stability of the M–Ccarbene bond in main group metal-imidazol-2-ylidene complexes: a computational and structural database study

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Samuel Tetteh ◽  
Albert Ofori
Keyword(s):  
Electron Density ◽  
Lone Pair ◽  
Main Group ◽  
Binding Energies ◽  
Electrostatic Model ◽  
Group Metal ◽  
Main Group Metal ◽  
Structural Database ◽  
The Stability ◽  
Lone Pair Electrons

Abstract The M–Ccarbene bond in metal (M) complexes involving the imidazol-2-ylidene (Im) ligand has largely been described using the σ-donor only model with donation of σ electrons from the sp-hybridized orbital of the carbene carbon into vacant orbitals on the metal centre. Analyses of the M–Ccarbene bond in a series of group IA, IIA and IIIA main group metal complexes show that the M-Im interactions are mostly electrostatic with the M–Ccarbene bond distances greater than the sum of the respective covalent radii. Estimation of the binding energies of a series of metal hydride/fluoride/chloride imidazol-2-ylidene complexes revealed that the stability of the M–Ccarbene bond in these complexes is not always commensurate with the σ-only electrostatic model. Further natural bond orbital (NBO) analyses at the DFT/B3LYP level of theory revealed substantial covalency in the M–Ccarbene bond with minor delocalization of electron density from the lone pair electrons on the halide ligands into antibonding molecular orbitals on the Im ligand. Calculation of the thermodynamic stability of the M–Ccarbene bond showed that these interactions are mostly endothermic in the gas phase with reduced entropies giving an overall ΔG > 0.

scholarly journals Long-term stability in γ-CsPbI3 perovskite via an ultraviolet-curable polymer network

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Nam-Kwang Cho ◽  
Hyun-Jae Na ◽  
Jeeyoung Yoo ◽  
Youn Sang Kim
Keyword(s):  
Polymer Network ◽  
Lone Pair ◽  
Ambient Conditions ◽  
Absorption Properties ◽  
Term Stability ◽  
Long Term Stability ◽  
Ultraviolet Curable ◽  
Oxygen Lone Pair ◽  
Lone Pair Electrons

AbstractBlack-colored (α, γ-phase) CsPbI3 perovskites have a small bandgap and excellent absorption properties in the visible light regime, making them attractive for solar cells. However, their long-term stability in ambient conditions is limited. Here, we demonstrate a strategy to improve structural and electrical long-term stability in γ-CsPbI3 by the use of an ultraviolet-curable polyethylene glycol dimethacrylate (PEGDMA) polymer network. Oxygen lone pair electrons from the PEGDMA are found to capture Cs+ and Pb2+ cations, improving crystal growth of γ-CsPbI3 around PEGDMA. In addition, the PEGDMA polymer network strongly contributes to maintaining the black phase of γ-CsPbI3 for more than 35 days in air, and an optimized perovskite film retained ~90% of its initial electrical properties under red, green, and blue light irradiation.

VUV FRAGMENTATION OF SOME HYDROFLUOROCARBON CATIONS STUDIED USING COINCIDENCE TECHNIQUES

2002 ◽  
Vol 09 (01) ◽  
pp. 153-158 ◽  
Author(s):  
WEIDONG ZHOU ◽  
D. P. SECCOMBE ◽  
R. Y. L. CHIM ◽  
R. P. TUCKETT
Keyword(s):  
Kinetic Energy ◽  
Ab Initio ◽  
Ground State ◽  
Lower Energy ◽  
Lone Pair ◽  
Electronic States ◽  
Photoelectron Spectra ◽  
Highest Occupied Molecular Orbital ◽  
Impulsive Model ◽  
Lone Pair Electrons

Threshold photoelectron–photoion coincidence (TPEPICO) spectroscopy has been used to investigate the decay dynamics of the valence electronic states of the parent cation of several hydrofluorocarbons (HFC), based on fluorine-substituted ethane, in the energy range 11–25 eV. We present data for CF 3– CHF 2, CF 3– CH 2 F , CF 3– CH 3 and CHF 2– CH 3. The threshold photoelectron spectra (TPES) of these molecules show a common feature of a broad, relatively weak ground state, associated with electron removal from the highest-occupied molecular orbital (HOMO) having mainly C–C σ-bonding character. Adiabatic and vertical ionisation energies for the HOMO of the four HFCs are presented, together with corresponding values from ab initio calculations. For those lower-energy molecular orbitals associated with non-bonding fluorine 2pπ lone pair electrons, these electronic states of the HFC cation decay impulsively by C–F bond fission with considerable release of translational kinetic energy. Appearance energies are presented for formation of the daughter cation formed by such a process (e.g. CF 3– CHF +), together with ab initio energies of the corresponding dissociation channel (e.g. CF 3– CHF + + F ). Values for the translational kinetic energy released are compared with the predictions of a pure-impulsive model.

The molecular orbital theory of chemical valency. V. The structure of water and similar molecules

1950 ◽  
Vol 202 (1070) ◽  
pp. 323-336 ◽  
Keyword(s):  
Spatial Distribution ◽  
Equilibrium Configuration ◽  
Bond Angle ◽  
Lone Pair ◽  
Orbital Theory ◽  
Hydrogen Atoms ◽  
Molecular Formation ◽  
Major Factors ◽  
Lone Pair Electrons ◽  
Electrostatic Repulsions

The theory of molecular and equivalent orbitals developed in previous papers of this series is used to discuss the spatial distribution of lone-pair electrons in molecules such as H 2 O and NH 3 and the part they play in determining the equilibrium configuration. Previous treatments of H 2 O have assumed that the lone pairs are essentially unaltered by molecular formation. It is shown here, on the other hand, that they will be displaced so as to be mainly concentrated on the side of the O-nucleus remote from the hydrogen atoms. An important consequence of this is that the lone-pair electrons will make a contribution to the total dipole moment. Comparison of the experimentally observed moment with an approximate quantitative treatment suggests that, as a result of this, transfer of electrons from the hydrogen atoms to the oxygen does not occur to the extent that has previously been believed. The variation of the spatial distribution of the orbitals of H 2 O with changes of nuclear configuration is examined and it is shown that, in the equilibrium position, the electronic structure can be described approximately by two sets of two equivalent orbitals pointing in nearly tetrahedral directions. The dependence of total energy on bond angle is discussed and it is shown that electrostatic repulsions between the equivalent orbitals are major factors in determining the equilibrium configuration. Similar considerations apply to NH 3 .

p-Type conductivity of GeTe: The role of lone-pair electrons

2012 ◽  
Vol 249 (10) ◽  
pp. 1902-1906 ◽  
Author(s):  
Alexander V. Kolobov ◽  
Paul Fons ◽  
Junji Tominaga
Keyword(s):  
Lone Pair ◽  
Type Conductivity ◽  
P Type ◽  
Lone Pair Electrons

Synergistic optimization of carrier transport and thermal conductivity in Sn-doped Cu2Te

2018 ◽  
Vol 6 (39) ◽  
pp. 18928-18937 ◽  
Author(s):  
Yuchong Qiu ◽  
Ying Liu ◽  
Jinwen Ye ◽  
Jun Li ◽  
Lixian Lian
Keyword(s):  
Thermal Conductivity ◽  
Fermi Level ◽  
Carrier Concentration ◽  
Power Factor ◽  
Carrier Transport ◽  
Lone Pair ◽  
Thermoelectric Performance ◽  
Degenerate Semiconductors ◽  
Lone Pair Electrons

Doping Sn into the Cu2Te lattice can synergistically enhance the power factor and decrease thermal conductivity, leading to remarkably optimized zTs. The lone pair electrons from the 5s orbital of Sn can increase the DOS near the Fermi level of Cu2Te to promote PF and reduce κe by decreasing the carrier concentration. This study explores a scalable strategy to optimize the thermoelectric performance for intrinsically highly degenerate semiconductors.

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