Molecular form factors in X-ray crystallography

Groenewegen, P.P.M.; Feil, D.

doi:10.1107/s0567739469000891

Cited by 12 publications

(8 citation statements)

References 3 publications

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“…The lowest agreement factor obtained by Groenewegen & Feil (1969), using a multicentre wavefunction for NH4 +, was R = 1.8 (R w = 2.6, four parameters refined). Bianchi et al (1977) were able to obtain a value R = 1.6 (R w = 2.2, nine parameters refined) for * The standard molecular-orbital exponent refers to a wavefunction.…”

Section: (C) Comparison With Molecular Wavefunction Modelsmentioning

confidence: 99%

“…(2) To carry out an analysis of the charge transfer within the ammonium ion and to assess the model dependence and significance of this analysis. (3) To compare the pseudo-atom model with the molecular wavefunction model of the ammonium ion used by Groenewegen & Feil (1969) and by Bianchi et al (1977). (4) To examine the physical significance of the electron distribution obtained for the hydrogens.…”

Section: Framework and Assumptions Of Present Studymentioning

confidence: 99%

“…This method was used to analyse the data of Adrian & Feil for NH4F by Groenewegen & Feil (1969) and, very recently, by Bianchi, Cremaschi, Morosi & Simonetta (1977). Groenewegen & Feil employed the accurate multicentre wave functions of Krauss (1963) for the isolated ammonium ion, while Bianchi et al used NH + wavefunctions obtained by ab initio SCF and SCF + CI methods, with both minimal and extended basis sets having standard or optimized exponents.…”

Section: Introductionmentioning

confidence: 99%

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Electron distribution and charge transfer in the ammonium ion

Mair¹

1978

Acta Cryst Sect A

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A re-analysis of the single-crystal X-ray data of Adrian & Feil [Acta Cryst. (1969), A25, 438-444] for ammonium fluoride has shown that there is a transfer of negative charge from the 'surface' of the ammonium ion to the central nitrogen. In addition to charge transfer, models used in the analysis allow for non-rigid-body motion of the ammonium ion and asphericity in the hydrogen electron densities. This asphericitiy has been represented in two different ways, one involving a floated monopole and the other a polarized distribution centred on the neutron-determined position. Both models give comparable fits to the data and similar chargetransfer parameters are obtained, so that the floated-monopole model is considered adequate for obtaining properties of the total molecular electron distribution. However, the dipole model is to be preferred if information about the hydrogen pseudo-atom is desired. The present analysis is compared with previous ones employing structure factors derived from molecular wavefunctions for the ammonium ion. These previous analyses are less successful than might be expected and this is attributed to their over-simplified treatment of the ammonium ion as a rigid body and their neglect of crystal-field effects.

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Section: (C) Comparison With Molecular Wavefunction Modelsmentioning

confidence: 99%

Section: Framework and Assumptions Of Present Studymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Electron distribution and charge transfer in the ammonium ion

Mair¹

1978

Acta Cryst Sect A

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“…This paper presents some new results obtained along the lines developed by G & F. The chemical bond in N2 and CN-is shown to be observable by X-ray diffraction. A preliminary report on this part has been given elsewhere (Groenewegen, 1969;Zeevalkink, 1970).…”

Section: Introductionmentioning

confidence: 99%

“…The molecular form-factor formalism, introduced in a previous paper (Groenewegen & Feil, 1969, henceforth referred to as G & F), resolves the electron density in solid-state structures in terms of molecules instead of atoms. This means that the scattering by a molecule is no longer given by the well known equation fmolecole(S) = ~ J~exp (is.…”

Section: Introductionmentioning

confidence: 99%

X-ray scattering and the chemical bond in N₂and CN⁻

Groenewegen¹,

Zeevalkink²,

Feil³

1971

Acta Cryst Sect A

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X-ray scattering from the chemical bond within Nz and CN-has been studied in detail. Differences in scattering from these systems, derived from bonding and non-bonding models, are characterized by R values of ~ 0.04. Partitioning of the scattering into core and valence electron parts clearly demonstrates that the bonding effects are completely situated in the valence electron structure of the systems. Therefore, new evidence has been contributed to support valence structure analysis methods presently employed in X-ray diffraction structure studies.

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