Elimination of extinction by a temperature gradient

Seiler, Paul; Dunitz, J. D.

doi:10.1107/s0567739478000595

Cited by 6 publications

(7 citation statements)

References 11 publications

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“…For example, detailed analysis of the shape of the azimuthal scan curves for a spherical sample of ammonium bitartrate crystal indicated that the shape of the curve, however periodical with 180° period of the b angle, is quite far from the expected smoothness. The observed variation of the integrated intensity for different azimuthal angles may be attributed to anisotropic extinction effects [12,13]. Denne [10] reports the observation of significant anisotropic extinction effects for α-glycine crystals.…”

Section: Extinction and Absorptionmentioning

confidence: 92%

Optimization of Azimuthal Scan Procedure for Absolute Structure Determination

Grochowski

Serda

1997

Acta Phys. Pol. A

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The paper describes the application of the azimuthal scan technique for absolute structure determination using X-ray anomalous dispersion. A diffraction pattern with rotation around the scattering vector provides information about various anisotropic effects: absorption, extinction and multi--beam interaction. Recording of azimuthal scans for Friedel pairs is proposed as an alternative to single reflection measurement. Several factors affecting the smoothness of the azimuthal scan curves are discussed and a procedure for eliminating various sources of errors, involving a Fourier filtering, is proposed in order to increase feasibility of chiral discrimination.

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Section: Extinction and Absorptionmentioning

confidence: 92%

Optimization of Azimuthal Scan Procedure for Absolute Structure Determination

Grochowski

Serda

1997

Acta Phys. Pol. A

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“…One should, however, take into account that the apparently shorter C-C bonds in the unsubstituted ring may be a result of the strong libration in this ring, as demonstrated by the elongated ellipsoids. Disorder of the Cp rings in ferrocene is a well known phenomenon which was initially described by Seiler & Dunitz (1979a). The longest Cp bonds are C1-C2 [1.437 (3) Å ] and C1-C5 [1.429 (3) Å ] vicinal to the substituent at C1 (Fig.…”

Section: Commentmentioning

confidence: 95%

“…Ferrocene exists in three polymorphic forms, one at room temperature, which is monoclinic (Seiler & Dunitz, 1979a;Takusagawa & Koetzle, 1979), and two at low temperature, viz. triclinic and orthorhombic (Seiler & Dunitz, 1979b, 1982.…”

Section: Commentmentioning

confidence: 99%

A new polymorph of 1-ferrocenyl-3-(3-nitroanilino)propan-1-one

et al. 2012

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Recrystallization of the title compound, [Fe(C(5)H(5))(C(14)H(13)N(2)O(3))], from a mixture of n-hexane and dichloromethane gave the new polymorph, denoted (I), which crystallizes in the same space group (P1) as the previously reported structure, denoted (II). The Fe-C distances in (I) range from 2.015 (3) to 2.048 (2) Å and the average value of the C-C bond lengths in the two cyclopentadienyl (Cp) rings is 1.403 (13) Å. As indicated by the smallest C-Cg1-Cg2-C torsion angle of 1.4° (Cg1 and Cg2 are the centroids of the two Cp rings), the orientation of the Cp rings in (I) is more eclipsed than in the case of (II), for which the value was 15.3°. Despite the pronounced conformational similarity between (I) and (II), the formation of self-complementary N-H···O hydrogen-bonded dimers represents the only structural motif common to the two polymorphs. In the extended structure, molecules of (I) utilize C-H···O hydrogen bonds and, unlike (II), an extensive set of intermolecular C-H···π interactions. Fingerprint plots based on Hirshfeld surfaces are used to compare the packing of the two polymorphs.

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“…VI), and the recent variations include asymmetric Bragg reflection (Mathieson, 1977b) and tilting the crystal about the scattering vector in the symmetrical Laue case (Lawrence & Mathieson, 1977). Also, spreading the reflecting power diffusely in reciprocal space may be included in this category, and in addition to mechanical introduction of strains in the crystal radiation defects (Sanger, 1969) and thermal gradients (Seiler & Dunitz, 1978) have also been employed.…”

Section: Introductionmentioning

confidence: 99%

Experimental correction for primary and secondary extinction. I. Method

Suortti¹

1982

Acta Cryst Sect A

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The energy transfer equations are used to solve secondary extinction in a parallel-sided crystal slab in Laue geometry. Practical formulas are given for determination of the refiectivity per unit length, tr(e), from the measured absolute powers of the diffracted and direct beams at rocking angle e = 0-0 B. The calculation assumes non-divergent beams, and the experimental tolerances are considered in detail. The primary extinction factor is defined by yp(e) = a(e)/Okin(e), where aki n is the kinematical reflectivity.When yp > 0.5 it may be approximated by yp ~_ exp[-(at~)2], where a is about 0.5 and fi is the average size of the coherent domains when measured in units of the extinction distance A, fi = D/A. The extinction distance can be varied by changing the X-ray wavelength or polarization, and yp(e) can be determined from two measurements.

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Elimination of extinction by a temperature gradient

Cited by 6 publications

References 11 publications

Optimization of Azimuthal Scan Procedure for Absolute Structure Determination

Optimization of Azimuthal Scan Procedure for Absolute Structure Determination

A new polymorph of 1-ferrocenyl-3-(3-nitroanilino)propan-1-one

Experimental correction for primary and secondary extinction. I. Method

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