Introduction to twinning

Parsons, Simon

doi:10.1107/s0907444903017657

Cited by 133 publications

(85 citation statements)

References 23 publications

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“…In certain cases, some of them pathological, these intensity distributions are perturbed; for example, merohedral twinning leads to changed intensity distributions and must be accounted for appropriately in structure solution (see Parsons, 2003 for a review of twinning phenomena). Multiple tests can be performed before the availability of an atomic model, thus permitting a fundamental validation of the experimental data, and further tests exploit information from the atomic model.…”

Section: Resultsmentioning

confidence: 99%

A New Generation of Crystallographic Validation Tools for the Protein Data Bank

et al. 2011

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SummaryThis report presents the conclusions of the X-ray Validation Task Force of the worldwide Protein Data Bank (PDB). The PDB has expanded massively since current criteria for validation of deposited structures were adopted, allowing a much more sophisticated understanding of all the components of macromolecular crystals. The size of the PDB creates new opportunities to validate structures by comparison with the existing database, and the now-mandatory deposition of structure factors creates new opportunities to validate the underlying diffraction data. These developments highlighted the need for a new assessment of validation criteria. The Task Force recommends that a small set of validation data be presented in an easily understood format, relative to both the full PDB and the applicable resolution class, with greater detail available to interested users. Most importantly, we recommend that referees and editors judging the quality of structural experiments have access to a concise summary of well-established quality indicators.

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Section: Resultsmentioning

confidence: 99%

A New Generation of Crystallographic Validation Tools for the Protein Data Bank

et al. 2011

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“…After several cycles of least-squares refinements, the quality of the crystal solution did not improve, and very large s.u.s were registered for the BASF parameter, which ultimately suggested that the structure is in fact not twinned. This was further confirmed by using the program ROTAX [39] (available with the software package CRYSTALS), [40] and also the TWINROTMAT routines implemented in PLATON.…”

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confidence: 79%

Photoluminescent Porous Modular Lanthanide–Vanadium–Organic Frameworks

et al. 2009

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Modular mixed metal‐organic frameworks with lanthanide centres,M4[M12V24O24(OH)8(H2hedp)8(Hhedp)16(H2O)64+n]·88+y(H2O) (M3+ = Y3+, Ce3+, Sm3+, Eu3+, Tb3+, Gd3+, Er3+; H5hedp = etidronic acid), have been reported. The compounds have been prepared by (i) slow evaporation of the solvent to afford large single‐crystals of the Y3+, Ce3+ and Er3+compounds and (ii) facile one‐pot synthesis (at ambient conditions) overnight to yield microcrystalline Y3+, Ce3+, Sm3+, Eu3+, Tb3+ and Gd3+ solids. Framework construction has been shown to be modular and based on the self‐assembly of cyclic trinuclear [V3O3(OH)(H2hedp)(Hhedp)2]6– anionic units with cationic {MO8} or {MO9} aqua‐based lanthanide complexes (with dodecahedral, square antiprismatic or tricapped trigonal prismatic coordination geometries), which gives rise to unprecedented trinodal networks (having 2‐ and 4‐connected nodes) with a total Schäfli symbol of {4.83.102}2{42.84}{8}2. The anionic charge of the networks is balanced by highly disordered trivalent lanthanide cations in the channels. The compounds have been studied by single‐crystal and powder X‐ray diffraction, vibrational spectroscopy (FTIR), thermogravimetry, optical and scanning electron microscopy and elemental analysis. The photoluminescence properties of selected compounds have been investigated. Intriguingly, the co‐existence of V4+ and Eu3+ cations in the same material allows the fine tuning of the photoluminescence emission from white to purplish‐blue, by changing the excitation wavelength.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

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“…[AgL]PF 6 (L ¼ 9, ON/NSN) The complex crystallises in monoclinic P2 1 /n with b being very close to 90 and the structure proved to be twinned by a twofold rotation about a thus emulating orthorombic symmetry (21). The twinning was accounted for by the use of the appropriate twin law during refinement.…”

Section: Synthesis Of Metal Complexesmentioning

confidence: 99%

Comparative investigation of the interaction of Zn(II), Cd(II), Ag(I) and Pb(II) with dibenzo-substituted macrocyclic ligands incorporating both symmetrically and unsymmetrically arranged N, O and S donors: synthetic, solution and X-ray studies

Vasilescu

Bourne

Clegg

et al. 2012

Supramolecular Chemistry

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Comparative investigation of the interaction of Zn(II), Cd(II), Ag(I) and Pb(II) with dibenzo-substituted macrocyclic ligands incorporating both symmetrically and unsymmetrically arranged N, O and S donors: synthetic, solution and X-ray studies, Supramolecular Chemistry, 24:8, 572-584, A comparison of the interaction of Zn(II), Cd(II), Ag(I) and Pb(II) with a matrix of 18, 17-membered, dibenzo-substituted macrocyclic ligands (1-18) incorporating nitrogen, oxygen and/or sulfur heteroatom sites that share the same carbon backbone is reported. Potentiometric log K data for complexes of these metals with 5, 6, 8 and 9 incorporating unsymmetric arrangements of their donor sets were obtained and the results compared with previously determined stability data for the remaining symmetrical and unsymmetrical ligand complexes forming the above matrix. Structure -function relationships underlying the relative magnitudes of the respective log K values are discussed, with emphasis given to the influence of both the donor atom set and the donor atom sequence on the nature of the resulting complexes. The X-ray structures of [CdL(NO 3 )] (NO 3 )·CH 3 CH 2 OH (L ¼ 4, SN 4 donor set), [CdL(NO 3 ) 2 ]·CH 3 OH (L ¼ 7, ON 4 donor set), [AgL]PF 6 (L ¼ 4, SN 4 donor set) and [AgL]PF 6 (L ¼ 9, OSN 3 donor set) are presented along with that of the metal-free diprotonated nitrate salt (LH 2 )(NO 3 ) 2 (L ¼ 6, S 2 N 3 donor set).

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Introduction to twinning

Cited by 133 publications

References 23 publications

A New Generation of Crystallographic Validation Tools for the Protein Data Bank

A New Generation of Crystallographic Validation Tools for the Protein Data Bank

Photoluminescent Porous Modular Lanthanide–Vanadium–Organic Frameworks

Comparative investigation of the interaction of Zn(II), Cd(II), Ag(I) and Pb(II) with dibenzo-substituted macrocyclic ligands incorporating both symmetrically and unsymmetrically arranged N, O and S donors: synthetic, solution and X-ray studies

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