scholarly journals Atomic radii from electron densities.

2000 ◽  
Vol 53 (2) ◽  
pp. 317 ◽  
Author(s):  
B. E. Etschmann ◽  
E. N. Maslen
Keyword(s):  
Angular Momentum ◽  
Bond Order ◽  
Free Atom ◽  
Nuclear Region ◽  
Electron Densities ◽  
Bond Lengths ◽  
Valence Electrons ◽  
Exchange Repulsion ◽  
Predicted Values ◽  
Atomic Radii

Bond lengths for diatomic molecules are predicted from atomic radii derived from free atom one-electron densities by postulating shielding factors for their valence electrons that depend on orbital angular momentum and on the bond order. The predicted values are closer to spectroscopically measured bond lengths than those based on earlier atomic radii inferred from a wider range of structural evidence. The bond lengths predicted by the sum of the atomic radii are corrected by a reduction that allows for charge transfer and by an extension associated with exchange repulsion of the overlapping electrons in the inter-nuclear region. Both corrections are related to free atom one-electron densities.

The Influence of the Chemical State on K x-RayIntensities

1984 ◽  
Vol 39 (10) ◽  
pp. 924-929 ◽  
Author(s):  
T. Rose ◽  
G. L. Borchert ◽  
O. W. B. Schult
Keyword(s):  
High Accuracy ◽  
Chemical State ◽  
Free Atom ◽  
X Ray ◽  
Quantum Numbers ◽  
Valence Electrons ◽  
Significant Intensity

The x-ray intensities of the Kβ and KO lines relative to the Kα1, transition were measured with high accuracy for the pairs La2O3-La, SmS-Sm, Sm2O3-Sm and Ta2O5-Ta. The Kβ13 and Kβ24 lines do not show significant intensity shifts. However, the intensity of the KO line is in La2O3 (15.0 ±4.7)% higher, in SmS (6.9 ± 2.7)% lower and in Ta2O5 (12.5 ± 8.7)% higher than that emitted from the corresponding metal. These results can be reproduced by Dirac-Fock-calculations, where the KO-intensities show a typical dependence on the quantum numbers of the valence electrons. The observed shifts indicate a 4f-5d hybridization or promotion in metallic Lanthanum and suggest the missing of a 4f electron in metallic Samarium compared to the free atom.

Bond order-bond length relationships in conjugated hydrocarbons - the microwave spectrum and structure of 3,4-dimethylenecyclobutene

1983 ◽  
Vol 36 (4) ◽  
pp. 639 ◽  
Author(s):  
RD Brown ◽  
PD Godfry ◽  
BT Hart ◽  
AL Ottrey ◽  
M Onda ◽  
...  
Keyword(s):  
Dipole Moment ◽  
Ab Initio ◽  
Bond Length ◽  
Bond Order ◽  
Microwave Spectrum ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Bond Orders ◽  
Bond Lengths ◽  
Typical Error

The microwave spectrum of the benzene isomer 3,4-dimethylenecyclobutene including spectra of all possible single 13C-substituted and sufficient singly and doubly D-substituted species to give a complete r5 geometry, have been measured and analysed. An estimate of the re geometry has also been derived. The additional precise CC bond lengths obtained for an unsubstituted, conjugated hydrocarbon enable us to examine bond order-bond length relationships more thoroughly than has previously been possible. The CC bond lengths exhibit a noticeably better correlation with SCFMO bond orders than with simple H�ckel bond orders. Further confirmatory measurements of the dipole moment of dimethylenecyclobutene have been made. Ab initio molecular orbital calculations using a 6-31G basis set give an optimized geometry with CC bond lengths within 2 pm of the r5 values. The computed dipole moment agrees almost exactly with experiment but a corresponding calculation on fulvene is discrepant with experiment by 0.16 D, which is probably a more typical error.

Accurate heats of atomization and accurate bond lengths.: II. Polyenes and polyphenyls

1968 ◽  
Vol 46 (12) ◽  
pp. 2041-2051 ◽  
Author(s):  
Donald H. Lo ◽  
M. A. Whitehead
Keyword(s):  
Steric Hindrance ◽  
Bond Order ◽  
Minimum Energy ◽  
Stabilization Energy ◽  
Direct Measure ◽  
Bond Lengths ◽  
Molecular Stability ◽  
Linear Polyenes ◽  
Substituted Polyenes ◽  
Good Agreement

Accurate heats of atomization and bond lengths are calculated for several polyenes and polyphenyls, using the s.c.f.–l.c.a.o.–m.o. method described in Part I (1). Localization of π and σ bonds is found in the linear polyenes and in the diphenyl-substituted polyenes. The estimated stabilization energy per CC bond (SECC) gives a direct measure of the π electron conjugation and σ bond compression. Conjugation stabilization and steric hindrance are analyzed in 1,3-butadiene and biphenyl; the predicted geometries are in good agreement with experimental results. The minimum energy for any planar structure is found to be associated with the s.c.f. calculated bond lengths. The validity of pi bond order as a measure of molecular stability in the polyphenyls is discussed.

Bond Lengths in Conjugated Molecules: The Present Position

1951 ◽  
Vol 207 (1088) ◽  
pp. 91-100 ◽  
Keyword(s):  
Bond Order ◽  
Empirical Relation ◽  
Simple Theory ◽  
Reliable Estimate ◽  
Present Position ◽  
Conjugated Molecules ◽  
X Ray ◽  
Bond Lengths ◽  
Hydrocarbon Molecules ◽  
Semi Empirical

A survey is given of the present methods for calculating bond lengths in conjugated molecules. Except in simple cases this has to be achieved by combining a calculated bond order with a semi-empirical relation between order and length. There are several definitions of bond order in current use, some of which can be shown to be less valuable than others. Recent accurate X -ray analysis has shown convincingly that the concept of bond order is a valid one, though there are limits to the degree of accuracy that may be claimed. Several possible improvements upon the simple theory are mentioned, most of which indicate alterations in bond lengths calculated from the simple theory, of the order of 0.005 Å. It is concluded that for condensed hydrocarbon molecules, the lengths of individual bonds may be predicted to within about 0.015 Å. For heteromolecules there are still too many additional factors for any reliable estimate to be possible.

scholarly journals Bond lengths in naphthalene and anthracene

1951 ◽  
Vol 207 (1090) ◽  
pp. 306-320 ◽  
Keyword(s):  
Aromatic Hydrocarbon ◽  
Bond Length ◽  
Configuration Interaction ◽  
Bond Order ◽  
Bond Orders ◽  
Bond Lengths ◽  
Self Consistent ◽  
Hydrocarbon Molecules ◽  
Experimental Values ◽  
Correction Terms

An extremely careful inquiry is made into the possibility of predicting bond lengths in condensed aromatic hydrocarbon molecules. Agreement with the best experimental values, such as those of Robertson, Abrahams, White, Mathieson and Sinclair, is fairly easily obtained to an accuracy of about 0.02Å. This shows that the concept of fractional bond order may quite properly be used to infer bond lengths. Both the molecular-orbital and resonance methods are equally good for this purpose. Predictions to within less than 0.02Å require the introduction of new factors usually neglected. No less than five such factors are discussed: ( а ) electrostatic forces, arising from possible differences in electronegativity of the various carbon atoms, ( b ) changes of bond orders due to electronegativity differences, ( c ) variation of resonance integrals with bond length, ( d ) obtaining a self-consistent set of resonance integrals, ( e ) inclusion of configuration interaction. Correction terms which result from these improvements lie between 0 and 0.015Å, and are not all of the same sign. It is unlikely therefore that this type of analysis will be able to give confident predictions of bond lengths to less than 0.01Å.

scholarly journals Chloroantimonate(III), IV. Darstellung und Kristallstruktur von 2,2′-Bipyridinium-pentachloroantimonat (C10H8N2H2)SbCl5 und der metastabilen Modifikation von 4,4′ -Bipyridinium-pentachloroantimonat (C10H8N2H2)SbCl5 / Chloroantimonates(III), IV. Preparation and Crystal Structures of 2,2′-Bipyridinium Pentachloroantimonate (C10H8N2H2)SbCl5 and of the Metastable Modification of 4,4′-Bipyridinium Pentachloroantimonate (C10H8N2H2)SbCl5

1983 ◽  
Vol 38 (12) ◽  
pp. 1615-1621 ◽  
Author(s):  
Annegret Lipka
Keyword(s):  
Single Crystal ◽  
Diffraction Analysis ◽  
Crystal Structures ◽  
Bond Order ◽  
X Ray Diffraction ◽  
X Ray ◽  
Bond Lengths ◽  
Distorted Octahedral ◽  
Intermolecular Contacts

2,2′-Bipyridinium pentachloroantimonate (III) and the metastable modification of 4,4′-bipyridinium pentachloroantimonate(III) were synthezised and investigated by single crystal X-ray diffraction analysis. The structures consist of 2,2′-bipyridinium and 4,4′-bipyridinium cations, respectively, and of pentachloroantimonate anions. With regard to bonding and short intermolecular contacts the coordination of the Sb atoms is distorted octahedral in both structures. Bond lengths of equivalent Sb-Cl bonds differ strongly within the structure of the 2,2′-bipyridinium salt (239.9 pm to 312.1 pm) and are not distinguishable from short intermolecular contacts (305.4 pm and 321.8 pm). In the structure of the 4,4′-bipyridinium salt, bond distances vary only from 240.9 pm to 267.8 pm and are clearly below intermolecular contacts at 318.2 pm. In spite of the different distances the total bond order for each Sb atom is 3. In the structure of the 2,2′-bipyridinium salt the anions build tetramers, whereas in the structure of the 4,4′-bipyridinium salt the anions form chains

A Correlation between Bond Length and Ionic Bond Order. Application to the Ylide–Ylene Problem

1975 ◽  
Vol 53 (20) ◽  
pp. 3040-3043 ◽  
Author(s):  
Myung-Hwan Whangbo ◽  
Saul Wolfe ◽  
Fernando Bernardi
Keyword(s):  
Bond Length ◽  
Bond Order ◽  
The Other ◽  
Atomic Charges ◽  
Bond Orders ◽  
Ionic Bond ◽  
Molecular Systems ◽  
Bond Lengths ◽  
Coulombic Repulsion ◽  
Overlap Population

The C—O and C—S bond lengths of the cations, radicals, and anions CH3O, CH3S, CH2OH, and CH2SH have been found not to correlate with the overlap populations of the C—X bonds. On the other hand, very satisfactory linear relations are observed with the ionic bond orders of the C—X bonds. It is suggested that, in certain molecular systems, it may be more meaningful to associate shortening of a bond A—B with greater coulombic attraction (or smaller coulombic repulsion) between the two point charges represented by the net atomic charges on the atoms A and B than with an increase in the overlap population between these atoms. It is noted that such an interpretation can account for the short C—P bond in a phosphonium ylide without resort to (p → d)π conjugation.

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