Valence Bond Analysis of the Lone Pair Bond Weakening Effect for the X−H Bonds in the Series XHn= CH4, NH3, OH2, FH

1996 ◽  
Vol 100 (16) ◽  
pp. 6463-6468 ◽  
Author(s):  
David Lauvergnat ◽  
Philippe Maître ◽  
Philippe C. Hiberty ◽  
François Volatron
Keyword(s):  
Valence Bond ◽  
Lone Pair ◽  
Pair Bond

Molecular force field for chlorine trifluoride

1965 ◽  
Vol 18 (3) ◽  
pp. 261 ◽  
Author(s):  
MG Krishna ◽  
K Ramaswamy ◽  
R Pichai
Keyword(s):  
Force Field ◽  
Force Constant ◽  
Lone Pair ◽  
Pair Interaction ◽  
Pair Bond ◽  
Approximate Relation ◽  
Lone Pairs ◽  
Bond Pair ◽  
Molecular Force ◽  
Molecular Force Field

An attempt has been made to modify the UBFF for chlorine trifluoride by taking into account the presence of lone pairs of electrons, on the lines suggested by Pariseau, Wu, and Overend. It was found that the lone-pair-bond-pair interaction is less than the lone-pair-lone-pair interaction which is considerably lower than the stretching force constant for the lone pair of electrons. An approximate relation between the above interactions was obtained.

scholarly journals On the Nature of the Bonding in Coinage Metal Halides

Molecules ◽  
2022 ◽  
Vol 27 (2) ◽  
pp. 490
Author(s):  
Slađana Đorđević ◽  
Slavko Radenković ◽  
Sason Shaik ◽  
Benoît Braïda
Keyword(s):  
Valence Bond ◽  
Lone Pair ◽  
Metal Halides ◽  
Covalent Bonds ◽  
Coinage Metal ◽  
Bond Pair ◽  
High Level ◽  
Copper Halides ◽  
Large Charge ◽  
Charge Shift

This article analyzes the nature of the chemical bond in coinage metal halides using high-level ab initio Valence Bond (VB) theory. It is shown that these bonds display a large Charge-Shift Bonding character, which is traced back to the large Pauli pressure arising from the interaction between the bond pair with the filled semicore d shell of the metal. The gold-halide bonds turn out to be pure Charge-Shift Bonds (CSBs), while the copper halides are polar-covalent bonds and silver halides borderline cases. Among the different halogens, the largest CSB character is found for fluorine, which experiences the largest Pauli pressure from its σ lone pair. Additionally, all these bonds display a secondary but non-negligible π bonding character, which is also quantified in the VB calculations.

On the valences of bonds in the oxycomplexes of Sn2+

2009 ◽  
Vol 65 (6) ◽  
pp. 684-693 ◽  
Author(s):  
I. David Brown
Keyword(s):  
Valence Bond ◽  
Lone Pair ◽  
Bond Valence ◽  
Ionic Charge ◽  
Acta Cryst ◽  
Pair Bonds ◽  
The Standard Model ◽  
Bond Valence Sum ◽  
Bond Valence Model ◽  
Atomic Valence

The differences between Wang and Liebau's [Wang & Liebau (2007). Acta Cryst. B63, 216–228] stoichiometric valence (atomic valence) and structural valence (bond-valence sum) observed in Sn2+ and other lone-pair cation oxycomplexes arises from their use of the Brese & O'Keeffe bond-valence parameters which are based on the assumption that the bond-valence parameter b = 0.37 Å applies to all bond types. According to the theory of the bond-valence model, the bond-valence sum is necessarily equal to the ionic charge, implying that in the Wang and Liebau model the ionic charges are equal to the structural valence. If charges are chosen equal to the stoichiometric valence, the bond-valence parameters for Sn2+—O bonds are R 0 = 1.859 Å, b = 0.55 Å. While both models are theoretically valid, only the standard model relates bond valences to the concept of atomic valence. Wang and Liebau's suggestion that cation–lone-pair bonds make a significant contribution to the valence sums is confirmed, but such bonds cannot account for the full difference between the stoichiometric and structural valences because they are present in only a few compounds.

Some wave functions for the four-electron threecentre bonding of four- and eight-π-electron systems

1974 ◽  
Vol 27 (4) ◽  
pp. 691 ◽  
Author(s):  
RD Harcourt ◽  
JF Sillitoe
Keyword(s):  
Molecular Orbital ◽  
Configuration Interaction ◽  
Electron Pair ◽  
Valence Bond ◽  
Pair Bond ◽  
Wave Functions ◽  
Electron Systems ◽  
Numerical Evidence ◽  
The One ◽  
Increased Valence

For symmetrical four-electron three-centre bonding units, the standard valence-bond (VB), delocalized molecular orbital (MO), increased-valence (IV) and non-paired spatial orbital (NPSO) representations of the electrons are Diagram O3, NO2- and CF2 with four π-electrons, and N3-, CO2 and NO2+ with eight π-electrons, have respectively one and two four-electron three-centre bonding units for these n-electrons. By means of Pople-Parr-Pariser type approximations, the MO, standard VB, IV and NPSO wave functions for these systems are compared with complete VB (or best configuration interaction) wave functions for the ground states. Similar studies are reported for the n-electrons of N2O. Further demonstration is given for the important result obtained elsewhere that the IV formulae must always have energies which are lower than those of the standard VB formulae, provided that the same technique is used to construct electron-pair bond wave functions. The extra stability arises because IV formulae summarize resonance between the standard VB formulae and long-bond formulae of the type Diagram As has been discussed elsewhere, the latter structure can make appreciable contributions to the complete VB resonance when its atomic formal charges are either zero or small in magnitude.If two-centre bond orbitals are used to construct the wave functions for the one-electron bond(s) and the two-electron bond(s) of IV formulae, then the IV and MO wave functions are almost identical for the symmetrical systems. Further numerical evidence is provided for this near-equivalence.

Molecular force field for bromine pentafluoride

1968 ◽  
Vol 46 (14) ◽  
pp. 2393-2397 ◽  
Author(s):  
M. G. Krishna Pillai ◽  
P. Parameswaran Pillai
Keyword(s):  
Force Field ◽  
Lone Pair ◽  
Pair Interaction ◽  
Pair Bond ◽  
Halogen Atoms ◽  
Bond Pair ◽  
Molecular Force ◽  
Molecular Force Field ◽  
Lone Pair Electrons

An attempt has been made to study the influence of lone pair electrons on the potential constants of BrF5 with a modified Urey–Bradley force field. It is found that the lone pair – bond pair repulsion is greater than the bond pair – bond pair repulsion. It is also concluded from a study of other molecules containing halogen atoms that the ratio of lone pair – bond pair interaction to bond pair – bond pair interaction is very nearly 1.23.

scholarly journals Reversible Öffnung von Metall-Metall-Bindungen: Quantitative Untersuchung des Ringöffnungsgleichgewichts von [Cp′(CO)2Mn]2SeAryl+ / Reversible Opening of Metal Metal Bonds: Quantitative Analysis of the Ring Opening Equilibrium for [Cp′(CO)2Mn]2SeAry1+

1991 ◽  
Vol 46 (6) ◽  
pp. 719-728 ◽  
Author(s):  
Patrizia Lau ◽  
Gottfried Huttner ◽  
Laszlo Zsolnai
Keyword(s):  
Quantitative Analysis ◽  
Steric Hindrance ◽  
Ring Opening ◽  
Valence Bond ◽  
Lone Pair ◽  
Metal Bond ◽  
Vis Spectroscopy ◽  
Metal Metal ◽  
Different Temperatures ◽  
Metal Bonds

The compounds [Cp′(CO)2Mn]2SeR+ are isoelectronic analogues of the well known “inidene”-species [LnM]ER (E = P, As, Sb, Bi). While these latter “inidene” compounds exist in an open form with no metal-metal-interaction and the main group atom in a trigonal planar environment allowing for a three-center-4π-system MEM, their isoelectronic selenium analogues generally show equilibria between the “inidene”-type metal metal non bonded forms and their metal metal bond closed cyclic isomers. In a valence bond picture the four electrons, delocalized in the three-center-4π-system of the open isomers, are localized in the closed ones: two in the metal metal bond and two as a lone pair at a pyramidally coordinated selenium center.The corresponding equilibria are quantitatively analyzed for [Cp′(CO)2Mn]2SeR+ (R =PCF3-C6H4 (1), PCH3-C6H4 (PToI) (2), °CH3—C6H4 (°Tol) (3)) by UV/VIS spectroscopy of their solutions at different temperatures. The ring opening process which corresponds to the reversible opening of a metal metal bond is found to be entropically driven with reaction-entropies of around 25 [JΚ-1mol-1]. Correspondingly, imposing steric hindrance on R, [Cp′(CO)2Mn]2SeMes+ (4) yields a stable bond opened “inidene”-type compound. Reducing steric hindrance in [Cp′(CO)2Mn]2Se′Pr+ (5) gives the bond closed form as the only detectable isomer.

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