Electron Density Distributions in Molecules

Hirshfeld, F. L.

doi:10.1080/08893119108032957

Cited by 36 publications

(30 citation statements)

References 138 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Features observed in difference-electron-density maps •P --P --Ppro of organic molecules on or near chemical bonds may safely be attributed to bonding effects; p denotes the actual electron density and Ppro the electron density of the free-atom promolecule model (Hirshfeld, 1991). The interpretation of the difference densities near a heavy atom may be more ambiguous since there 3p may peak sharply at small distances from the atomic center.…”

Section: Introductionmentioning

confidence: 99%

Anharmonic MotionvsChemical Bonding: on the Interpretation of Electron Densities Determined by X-ray Diffraction

Restori¹,

Schwarzenbach²

1996

Acta Cryst Sect A

View full text Add to dashboard Cite

Anharmonic and electron-density ref'mements against accurate X-ray diffraction data are today almost routine. However, the unambiguous identification and separation of effects due to anharmonic atomic motion and to chemical bonding is impossible with a single X-ray data set and difficult even with data measured at different temperatures, especially in heavy-atom compounds. For cubic site symmetry, analytical expressions are compared for the convolutions of: (i) the electron density of a spherical free atom with an anharmonic probability density distribution (p.d.f.); and (ii) an aspherical atom with a Gaussian p.d.f. If both the free atom and the deformation functions of the aspherical atom are represented by Gaussian-type functions, there exists for every set of anharrnonic parameters an equivalent set of aspherical-atom parameters but the reverse is not necessarily true. Both models are usually suitable for parametrizing anharmonicity also in the case of real atoms and exponential-type deformation functions. Contrary to widespread belief, both models predict a qualitatively similar change of the aspherical density with decreasing temperature: the extrema move towards the atom center and their heights increase except at low temperatures. Quantitatively, however, the temperature dependence of the adjusted parameters should be different: in the case of anharmonicity, the second-, third-and fourth-order coefficients should be proportional to T, T 2 and T 3, respectively, while the population factors of the deformation functions should be independent of T. The theory is tested and verified with refinements on calculated and on measured X-ray structure amplitudes for K2PtC16 at room temperature and at 100K, and Si at room temperature. Results for KzPtC16 agree well with the anharmonic model. In Si at room temperature, the two effects overlap only slightly and can be reasonably well identified; they cannot be distinguished with simulated high-temperature data.

show abstract

Section: Introductionmentioning

confidence: 99%

Anharmonic MotionvsChemical Bonding: on the Interpretation of Electron Densities Determined by X-ray Diffraction

Restori¹,

Schwarzenbach²

1996

Acta Cryst Sect A

View full text Add to dashboard Cite

show abstract

“…However, to the author's knowledge, no detailed theoretical insight into the above problem has been gained up to date for complex organic molecules as well as for those of biological interest, although some attempts have been mentioned in [1].…”

Section: Introductionmentioning

confidence: 97%

“…Then the ground state of the polyatomic moiety in question is a succession of transitions between various fragmentation patterns. If the lifetime of some fragmentation pattern is greater than the characteristic time-scale of the X-ray diffraction measurement, one can observe no electron density between the corresponding atoms, as noted in [1].…”

Section: Introductionmentioning

confidence: 97%

“…The former factor significantly hinders dividing a crystal into molecules, taking the molecules within crystals into atoms and determining the ionicity of the atoms thus revealed, especially when one deals with X-ray patterns from crystals with polar molecules, H-bonding and/or polyatomic cation/anion ingredients. Based upon the numerous findings, a review [1] calls into question even the Heitler-London model of covalent bonding in molecules other than hydrogen. Specifically, high-resolution X-ray diffraction measurements often fail to reveal an accumulation of electron density between atoms which ought to be covalently bonded in accordance with trivial chemical intuition.…”

Section: Introductionmentioning

confidence: 98%

“…A great deal of high-resolution X-ray diffraction studies show that even in crystals of relatively simple compounds the observed electron density differs from the theoretical static density defined via the Born-Oppenheimer approximation because of intermolecular interactions and vibrational smearing [1]. The former factor significantly hinders dividing a crystal into molecules, taking the molecules within crystals into atoms and determining the ionicity of the atoms thus revealed, especially when one deals with X-ray patterns from crystals with polar molecules, H-bonding and/or polyatomic cation/anion ingredients.…”

Section: Introductionmentioning

confidence: 98%

See 2 more Smart Citations

On the electronic subsystem of nucleic acid crystallohydrates

Starikov¹

1993

Molecular Physics

View full text Add to dashboard Cite

The charge distribution of the mononucleotides within a number of the corresponding sodium-salt crystallohydrates has been estimated using the semiempirical quantum-chemical complete neglect of differential overlap (CNDO)/2-spd technique. The chemically conventional mononucleotide dianions cannot be theoretically 'enucleated' from some of the crystallohydrates under study. Based upon the thorough analysis of these results and comparison of them with the literature data, the idea of a 'travelling broken bond' describing the ground state of a mononucleotide within the sodium salt crystallohydrate is discussed.

show abstract

Organoalkali Reagents

Schlosser

1994

Organometallics in Synthesis

View full text Add to dashboard Cite

Electron Density Distributions in Molecules

Cited by 36 publications

References 138 publications

Anharmonic MotionvsChemical Bonding: on the Interpretation of Electron Densities Determined by X-ray Diffraction

Anharmonic MotionvsChemical Bonding: on the Interpretation of Electron Densities Determined by X-ray Diffraction

On the electronic subsystem of nucleic acid crystallohydrates

Organoalkali Reagents

Contact Info

Product

Resources

About