Valence electron distribution in cubic tetracyanoethylene by the combined use of x-ray and neutron diffraction

Becker, Pierre; Coppens, P.; Ross, F. K.

doi:10.1021/ja00804a010

Cited by 80 publications

(48 citation statements)

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“…A comparable but less pronounced effect is apparent in the other cyclic C-C bonds. Similar observations have been made in a number of other compounds [e.g., sym-triazine (Coppens, 1967); tetracyanoethylene (Becker, Coppens & Ross, 1973), and a series of hydrocarbons (Irngartinger, Leiserowitz & Schmidt, 1970)]. …”

Section: Valence-and Deformation Densitiessupporting

confidence: 80%

“…It is evident that the height of the lone-pair features on the O atoms increases with data cut-off, the lone-pair peaks in the full-data Fourier map being almost twice as high as in the low-angle function. The change in the bond density is much less pronounced, as would be expected on the basis of considerations given earlier (Becker, Coppens & Ross, 1973;Coppens, 1969). Unfortunately, the full data maps have an unusually high noise level in areas away from the bonding and lonepair regions.…”

Section: Valence-and Deformation Densitiesmentioning

confidence: 64%

“…5 and 6) neutral spherical atoms are subtracted from the observed density. In earlier room-temperature work evidence was obtained for the persistence of the lone-pair scattering into the high-order region (Becker, Coppens & Ross, 1973). It is therefore of interest to examine the effect on the lone-pair peak heights in the present study in which an unusually large number of highorder reflections are available.…”

Section: Valence-and Deformation Densitiesmentioning

confidence: 93%

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Charge density studies below liquid nitrogen temperature: X-ray analysis of p-nitropyridine N-oxide at 30 K

Wang¹,

Blessing²,

Ross³

et al. 1976

Acta Crystallogr Sect B

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The structure of p-nitropyridine N-oxide has been redetermined at both 30 and 300K. Data were collected in a step-scan mode and intensities obtained through profile-analysis. The b axis, which is normal to the molecular planes, contracts considerably on cooling, and thermal parameters decrease by a factor of about six, in agreement with predictions based on a simple harmonic model. The orientation of the thermal ellipsoids is essentially the same at both temperatures. Comparison of bond lengths at the two temperatures clearly demonstrates the necessity of a bond-length correction for shortening due to thermal motion. Bond lengths agree well after correction according to a rigid-body model. Difference densities were calculated with positional parameters and hydrogen thermal parameters from an independent low-temperature neutron study. Densities calculated with data cut-offs of sin 0/2= 0.65, 0.75, and 1/~-1 indicate an appreciable increase in noise level on inclusion of high-order reflections. The height of the lone-pair density increases with data cut-off while the densities in the bond regions are much less affected, thus confirming the hypothesis that the lone-pair electrons contribute to high-order scattering. Similarly, difference maps based on a high order X-ray refinement (sin 0/2 > 0.75 A-1) underestimated the density in the lone-pair regions.

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Section: Valence-and Deformation Densitiessupporting

confidence: 80%

Section: Valence-and Deformation Densitiesmentioning

confidence: 64%

Section: Valence-and Deformation Densitiesmentioning

confidence: 93%

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Charge density studies below liquid nitrogen temperature: X-ray analysis of p-nitropyridine N-oxide at 30 K

Wang¹,

Blessing²,

Ross³

et al. 1976

Acta Crystallogr Sect B

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“…The electron density analysis of TCNE with both Xray and neutron diffraction data has been described previously (Little, Pautler & Coppens, 1971;Becker, Coppens & Ross, 1973). As the severe extinction was originally treated with the Zachariasen formalism, both X-ray and neutron refinements have been repeated with the modified formalism of Becker & Coppens (1975).…”

Section: (B) Tetracyanothylene (Tcne)mentioning

confidence: 99%

Testing aspherical atom refinements on small-molecule data sets

Hansen¹,

Coppens²

1978

Acta Cryst A

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1,664

1,478

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X-ray data on silicon, tetracyanoethylene, p-nitropyridine N-oxide and ammonium thiocyanate are refined with a generalized aspherical-atom formalism as introduced by Stewart, but modified to have a spherical valence more similar to the unperturbed HF valence shell. Several types of radial dependences of the multipole functions are tested and criteria are developed for judging the adequacy of the aspherical-atom refinement. The aspherical-atom model leads to a significant decrease in the least-squares error function, a reduction of features in the residual map, and an improvement in thermal parameters when comparison is made with the neutron results or when the rigid-bond postulate proposed by Hirshfeld is applied. Positional parameters are often improved except in the case of terminal atoms for which discrepancies, attributed to correlation between dipole-population and positional parameters, are sometimes observed. Deformation maps based on the aspherical-atom least-squares parameters contain less noise than X --N maps and benefit from inclusion of calculated values of weak structure amplitudes in the summation. In the cases studied, deformation maps including terms beyond the experimental resolution do not yield additional information.

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“…A significant X-N positional shift of O(H) in oxalic (~ 1986 International Union of Crystallography acid dihydrate was noted by Coppens, Sabine, Delaplane & Ibers (1969); the C--C bond in tetracyanoethylene is foreshortened by some 0.01/~ in the X study (Little, Pautler & Coppens, 1971) by comparison with N (Becker, Coppens & Ross, 1973); X-foreshortening of phenyl-ring bond lengths are discussed by O'Connell, Rae & Maslen (1966). Coppens (1974) used X-N comparisons of structures available at that time to examine the magnitude and direction of positional shifts for first-row elements (C, N, O) in asymmetric bonding environments.…”

Section: Introductionmentioning

confidence: 98%

A systematic pairwise comparison of geometric parameters obtained by X-ray and neutron diffraction

Allen¹

1986

Acta Crystallogr B Struct Sci

188

120

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The effects of X-ray atomic asphericity on derived molecular geometry have been examined for ten common substructures involving C, N, O. The Cambridge Structural Database has been used to locate pairs of X-ray (X) and neutron (N) structure determinations of the same compound. Rigid criteria based on experimental temperature, refinement procedures, crystalline form and precision have been applied in selecting suitable X, N structure pairs. Corresponding X and N values for derived parameters have been paired for 46 chemically unique subsets (39 bond-length sets and 7 valence-angle sets). The statistical significance of the distribution of X-N differences (Di) has been assessed in each case via a Wilcoxon matched-pairs

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Valence electron distribution in cubic tetracyanoethylene by the combined use of x-ray and neutron diffraction

Cited by 80 publications

References 0 publications

Charge density studies below liquid nitrogen temperature: X-ray analysis of p-nitropyridine N-oxide at 30 K

Charge density studies below liquid nitrogen temperature: X-ray analysis of p-nitropyridine N-oxide at 30 K

Testing aspherical atom refinements on small-molecule data sets

A systematic pairwise comparison of geometric parameters obtained by X-ray and neutron diffraction

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