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Volumn 5, Issue 3, 2004, Pages 414-418

Challenges in direct-space structure determination from powder diffraction data: A molecular material with four independent molecules in the asymmetric unit

Author keywords

Direct space techniques; Genetic algorithms; Hydrogen bonds; Structure elucidation; X ray diffraction

Indexed keywords

GENETIC ALGORITHMS; HYDROGEN BONDS; X RAY DIFFRACTION;

EID: 2442524123     PISSN: 14394235     EISSN: None     Source Type: Journal    
DOI: 10.1002/cphc.200301078     Document Type: Article
Times cited : (63)

References (47)
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    • note
    • α1 (Gemonochromated); linear position-sensitive detector covering 8° in 2θ; 2θ range, 5-65°; step size, 0.019°; data collection time, 10 h].
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    • 1H decoupling (using the TPPM sequence with a decoupling field strength of ca. 100 kHz) and magic-angle sample spinning (with spinning frequency of 1500 ± 3 Hz). The sample temperature was set to 25°C and the recycle delay was 120s.
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    • This conclusion follows from the presence of two resonances in 1:1 intensity ratio for the carboxylic acid carbon of BA at ca. 166.5 ppm and two resonances in 1:1 intensity ratio for the carboxylic acid carbon of PFBA at ca. 173.8 ppm.
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    • note
    • Note that space group C2/c, which has the same systematic absences as Cc, has Z = 8 and would therefore give rise (with two molecules of BA and two molecules of PFBA in the asymmetric unit) to 16 molecules of BA and 16 molecules of PFBA in the unit cell, which would correspond to an unreasonably high density.
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    • note
    • The GA structure solution calculation involved two subpopulations, each comprising 50 trial structures. In each generation, 25 mating operations and 12 mutation operations were carried out for each subpopulation.
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    • note
    • The Rietveld refinement calculations explored whether the C-O bond lengths in the carboxylic acid groups are equal (representing disorder involving two orientations of the -COOH group, as often observed for carboxylic acid dimers) or different (representing distinguishable C-OH single and C = O double bonds), although no significant discrimination was obtained. The disordered model (with the carboxylic acid hydrogen atom omitted) was used in the final refinement calculations.
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    • note
    • p = 4.27%; 154 refined variables; 3094 profile points.
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    • note
    • 1 at which this torque due to intermolecular repulsive interactions is balanced by the restoring force that arises from the intramolecular (conformational) potential energy.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.