Notes for authors 2009

Notes for authors.


Submission requirements 1.Manuscript checking and preparation
All papers must be submitted in Crystallographic Information File (CIF) format. Details about CIFs are given in Hall et al. [Acta Cryst. (1991), A47, 655-685]. Guidelines for the preparation and editing of a CIF, the data items required therein, standard data codes and keywords, CIF templates, example CIFs, and data-validation criteria and procedures are available via the online author help page (see x8). A CIF editor for authors, publCIF, may be obtained from http:// journals.iucr.org/e/services/cif/publcif/, and a general CIF editor (enCIFer) may be obtained from http://www.ccdc.cam.ac.uk/products/ encifer/index.html; both editors are available free of charge. The Section Editors, Co-editors and Editorial Office staff are also available to assist any author with any technical CIF problems. Please note that this help does not include rewriting papers which do not reach the standards specified in x1.10.
Authors are required to pre-check their submission using the checkCIF service at http://journals.iucr.org/services/cif/checking/ checkfull.html. Any reported problems with the submitted data should normally be corrected before submission. If the report contains validation alerts about the consistency, adequacy or quality of the data, these will need to be addressed, or, if the authors consider there are specific valid or unavoidable reasons for these alerts, the validation response form (VRF) supplied by checkCIF should be completed and included in the submitted CIF, preferably with the addition of appropriate explanatory text in the deposited experimental section of the CIF.
The text and tables of a paper may be previewed by sending the CIF (after completing the pre-check) to the printCIF service at http:// journals.iucr.org/services/cif/printcif.html or by using publCIF. We strongly encourage authors to make use of this facility for checking the formatting of the supplementary materials.

Categories of submission
Section E publishes two categories of papers. The requested category must be specified in the submitted CIF as _publ_requested_ category, using one of the codes listed below.
(a) Short structural papers describe the determination of a single structure. The submitted CIF is validated using checkCIF and database checks are applied using the Inorganic Crystal Structure Database or the Cambridge Structural Database. The CIF, the checking results and associated files are then passed to a Co-editor for peer review. Once accepted, the paper and associated graphics, together with the CIF and structure factors, will be accessible electronically from the Crystallography Journals Online service at http://journals. iucr.org. The category codes used to identify these papers are EI for inorganic, EM for metal-organic, and EO for organic structures.
(b) Addenda or Errata are short papers describing additions to, comments on, or errata to existing Section E publications and are not intended for interim reports of work in progress. The text should not exceed 1000 words. Addenda and Errata are peer reviewed. The category code for these papers is AD.

Method of submission
Full details of the submission procedure can be found at http:// journals.iucr.org/e/services/helpsubmit.html. CIFs must be submitted via the web at http://journals.iucr.org/e/services/submitbdy.html. All submitted CIFs must have been pre-checked using the facilities described in x1.1.
During the submission procedure, authors will be required to submit additional electronic files; these include the chemical scheme (see x2.8), crystallographic diagrams (see x3.5) and structure factors (see x3.8) or powder diffraction data (see x3.7). Authors will also be asked to agree to an open-access licence (see x1.11). In addition, they will also be asked to confirm that they can pay the open-access fee, or that they have a payment waiver (see x9).
On completion of the submission procedure, each paper will be assigned an Editorial Office refcode. The Editorial Office refcode has two letters and four digits (e.g. hb3795), with the two letters identifying the assigned Co-editor; the refcode should be used in all subsequent communications with the Editorial Office and Coeditor.

Handling of manuscripts
Each submitted CIF is automatically validated for completeness and data integrity, and checked for duplication. If incomplete or inadequate it will be returned to the contact author for correction. Some of the specific data standards are summarized in x4, while full details of the required data items and the data-validation criteria are available via the online CIF help page (see x8). For papers failing to meet these criteria, a completed validation response form (VRF) giving reasons for the failure must be included in the CIF. The Coeditor will assess the validity of the explanation as part of the review process.
The Co-editor is responsible for the review steps and future communications with the authors up to the acceptance stage. If, after review, no revisions are necessary, the paper will be prepared for immediate electronic publication. If the review reveals that revision is required, the authors will be contacted directly and asked to revise the paper. Further revisions may be requested before acceptance of the submission if unresolved issues remain. When the paper is accepted by the Co-editor, the author will be asked to review the edited CIF and the HTML supplement, and approve these before proofs are prepared. The author will also be asked to pay the openaccess fee or provide a waiver at this stage.
Failure to respond to a communication from either a Co-editor or the Editorial Office staff within one month will result in the automatic withdrawal of the paper. All communications to authors will normally be sent electronically to the e-mail address provided in the CIF. Authors who anticipate or become aware of difficulties with their e-mail service should alert their Co-editor as soon as they are aware that there is a problem. If major revisions (i.e. revisions involving a complete new CIF) are made to the submission, the journal reserves the right to reset the date of receipt of the paper to the date of resubmission. If a manuscript is not acceptable after two revisions it will not be considered further. A paper that has been rejected must not be resubmitted to any IUCr journal unless the reasons given for the rejection have been fully addressed in the revised version.
Once a paper is accepted, it is the responsibility of the Managing Editor to prepare the paper for publication and to correspond with the authors and/or the Co-editor to resolve publication ambiguities or inadequacies. The Section Editors review all accepted papers and reserve the right to make minor changes to ensure conformity with Section E standards; in the unlikely event of significant changes being required at this stage, the authors will be contacted promptly.

Revisions
After initial submission, any revised or new files should be uploaded via the web interface only after a specific request from a Co-editor; these resubmitted files should be uploaded at the web address provided by the Co-editor.

Author's warranty
The submission of a paper is taken as an implicit guarantee that the work is original, that it is the author(s) own work, that all authors concur with and are aware of the submission, that all workers involved in the study are listed as authors or given proper credit in the acknowledgements, that the manuscipt has not already been published (in any language or medium), and that it is not being considered and will not be offered elsewhere while under consideration for an IUCr journal. The inclusion of material in an informal publication, e.g. a preprint server or newsletter, does not preclude publication in an IUCr journal.
The co-authors of a paper should be all those persons, and only those persons, who have made significant scientific contributions to the work reported, including the ideas and their execution, and who share responsibility and accountability for the results. Other contributions should be indicated in an Acknowledgements section. An administrative relationship to the investigation does not in itself qualify a person for co-authorship (but it may be appropriate to acknowledge major administrative assistance).
Important considerations related to publication have been given in the ethical guidelines published in Acc. Chem. Res.

Submission of related structures
To allow handling of papers to be automated, all submissions should report single structures only. Series of single structure papers on closely related materials should not be merged. It is possible for submissions reporting related structures to be handled together and published as adjacent papers. Authors should select the same Coeditor for each paper during submission. However, such studies may be more appropriately reported as a single paper in Acta Crystallographica Sections B or C. Papers in a series should cross-reference each other.

Previously published structures
If a structure has been redetermined correctly and the result adds significantly to the information already in the public domain then the paper can be considered for publication. Redeterminations that report a small improvement in precision or are merely carried out at a different temperature to previous studies will not normally be considered for publication. Unless they lead to significant insight, for example into reaction mechanisms or biological processes, determinations of the second enantiomer of a published first enantiomer of a structure will not be considered for publication. Redeterminations must cite the previous structure(s) and the Abstract must briefly state the changes and/or improvements attained.

Languages of submission
The languages of publication are English, French, German and Russian. Submissions in English may use either British or American spelling, but must do so consistently throughout.

Quality of writing
Papers must be clearly written and grammatically correct. If the Co-editor concludes that language problems would place an undue burden on the referee(s), the manuscript may be returned to the authors without review. Details of language-editing services can be found at http://journals.iucr.org/services/languageservices.html.

Copyright
Authors will not be asked to transfer copyright to the IUCr, but will instead be asked to agree during article submission to an openaccess licence. This licence is identical to the Creative Commons Attribution Licence.

Author grievance procedure
An author who believes that a paper has been unjustifiably treated by the Co-editor may appeal initially to the Section Editors for a new review and, finally, to the Editor-in-Chief of IUCr Journals if the author is still aggrieved by the decision. The initial appeal must be made within 3 months of rejection of the paper. The decision of the Editor-in-Chief is final. Any resubmission to another Co-editor will be forwarded to the Section Editors.

Publication requirements
The publication requirements for the text, tabular and graphical material are described in this section. Requirements for supplementary materials are given in x3, and the standards for numerical and codified data are summarized in x4. A list of all data items required for submission is available via the online CIF help page (see x8) where guidelines concerning the use of special characters (e.g. Greek letters and diacritical marks) and a set of Frequently Asked Questions are also given. Note that in the shorter article format the Related literature section (x2.3) replaces the Comment section; the Comment section, the Experimental text sections and the crystallographic diagrams now form part of the supplementary materials (x3). A chemical structural diagram must be included for molecular compounds (x2.8).

Title and authors
The Title should be short and informative; in many cases just the name of the compound studied will be perfectly adequate. However, the use of titles consisting of only the chemical formula is discouraged. Avoid complicated IUPAC names and redundant phrases such as 'Crystal structure of . . . '. For papers describing powder, neutron or synchrotron diffraction studies, the title should typically consist of the name of the compound followed by '(powder study)', '(neutron study)' or '(synchrotron study)', respectively. The full first name of each author is preferred. Note that the data items _publ_section_ title_footnote and _publ_author_footnote are available, if required, for inserting footnotes to the title and to individual authors. If the paper describes the redetermination of a previously reported structure, this should be indicated in the title. Part numbers for a series of related papers are not permitted in the title, but may be given as a title footnote.

Abstract
The Abstract must be written in English, be informative, and should summarize the most important aspects of the study. It is expected to be no more than 250 words and should be capable of being understood on its own without access to the text or figures. It should not contain the crystal data or, usually, the space group. The systematic IUPAC name and the chemical formula should be given here, if they are not included in the Title. The Abstract should include mention of any crystallographically imposed symmetry or the presence of more than one molecule (or formula unit) in the asymmetric unit of the structure. Principal structural geometry results can be given here. Literature references should be avoided if possible; if required, they must be given in full, e.g. [Bond, Davies & Kirby (2001). Acta Cryst. E57, o1242-o1244].

Related literature
All articles should include a Related literature section. Essential references (e.g. to the origin of the material studied, related structural studies, and to information supporting the reported structure) should be cited in this section, with appropriate very brief explanatory text, for example 'The synthesis of the complex is described by Jones (2001). The anhydrous complex has essentially the same coordination geometry (Smith, 2003).' In addition, all references included in the supplementary materials, but not elsewhere in the published article, should be given here. It is most useful for readers if the Related literature section is sub-divided, so that, instead of just "For related literature, see . . . ." it gives, for example, "For general background, see . . . . For related structures, see . . . ." etc.

Experimental data
Principal experimental data are extracted automatically from the CIF and are tabulated under the sub-headings Crystal data, Data collection and Refinement. Some numerical items may be formatted so that a standard number of decimal places is published. The full set of data in the CIF, as well as the content of the text sections _publ_section_exptl_prep, _exptl_special_details, _publ_ section_exptl_refinement and _refine_special_details, will be provided in the supplementary materials.

Acknowledgements
Acknowledgement should be given for any assistance provided to the study (see x1.6).

References
References to published work must be cited in the format detailed in x7. If reference is made to unpublished work, prior consent must be first obtained from the authors of that work.

Selected geometrical data
Full details of molecular dimensions, including those involving H atoms, should be supplied; only values that are of special interest should be flagged for publication by setting the _geom_..._flag value to yes. The data to be published in the paper will be reviewed by the Co-editor and a Section Editor.

Chemical scheme
A chemical structural diagram (typical examples are shown below) must be included for all but inorganic materials. Authors are required to submit such diagrams electronically in one of the formats listed in x5. The diagram should be complete, showing all species present in the structure, including counter-ions and solvent molecules in their correct proportions. The relative or absolute stereochemistry must be shown and should be consistent with the Crystallographic diagram (x3.5), the data reported in the Abstract (x2.2), Related literature (x2.3), Comment (x3.1) and Title (x2.1). Hydrogen bonding should not normally be indicated in the diagram.
The chemical structural diagram should show only the compound whose structure is being reported. Chemical reaction schemes or schemes showing more than one compound should be supplied as supplementary figures and should have appropriate captions included in _publ_section_figure_captions (see x5.4).

Powder diffraction data
Authors of powder diffraction papers should consult the notes provided at http://journals.iucr.org/services/cif/powder.html.

Standard uncertainties
The standard uncertainty (abbreviated s.u. and replacing the traditional term estimated standard deviation) should be expressed as a number in parentheses following the numerical result and should be on the scale of the least significant digits of the result. The s.u. value should preferably be in the range 2-19. Note that s.u. values should not be appended to parameters which are fixed by symmetry, geometry or other constraints.

Supplementary materials requirements
Section E provides extensive supplementary materials for each article. They include the supplementary data files (CIF, structure factors etc.), as well as (a) HTML and PDF representations of the deposited CIF and (b) the crystallographic diagrams. All supplementary materials will be available from Crystallography Journals Online (see x8). The text sections of the supplementary material (see xx3.1 and 3.2) will be only lightly edited and checked for obvious factual errors, and authors may be asked to provide revised text if necessary.

Comment
Where the submitted CIF includes a Comment section, this will be made available to readers in the HTML and PDF representations of the deposited CIF. Inclusion of a Comment section is strongly encouraged, especially to provide further information about the relevance of the Related literature and for discussion of the main structural results and their wider scientific context and significance, but the number of literature references should be small. The Comment section should also include a brief description of each crystallographic diagram (x5.1) provided by the authors.

Experimental text sections
The content of the text sections _publ_section_exptl_prep, _exptl_special_details, _publ_section_exptl_refinement and _refine_special_details will be included in the HTML and PDF representations of the deposited CIF. The descriptive text item _publ_section_exptl_prep is the appropriate place to give information on the chemical and crystal preparation, and identification (e.g. on melting points and densities), the inclusion of which is encouraged. Additional details [e.g. lengthy synthetic descriptions and long lists of spectroscopic (NMR, IR etc.) data] supporting the crystallographic study should be placed in the _exptl_special_ details section of the CIF. The text item _publ_section_exptl_ refinement should be used to provide details of how H atoms were treated and report the ranges of X-H dimensions. Any unusual aspects of the data collection, space-group identification, data processing, structure determination and refinement (including any restraints used and the treatment of disorder) should also be given here. Routine material should be placed in _refine_special_ details.

Atomic sites
The _atom_site_ coordinate and displacement parameters must be supplied with standard uncertainty values (see x2.10). The parameter constraints and restraints applied to the refinement process, and the anisotropic atomic displacement parameters (as U ij ) must also be supplied. Note that only U or U ij values are acceptable for atomic displacement parameters. The atom numbering should follow some recognized scheme (see x6.1) and the atom list should be in some sensible (not random) order. H-atom labels should be directly related to the atom to which they are bonded.

Geometrical data
Full details of molecular dimensions, including those involving H atoms, should be supplied. All submitted geometry data will be available to readers from Crystallography Journals Online. The inclusion of torsion angles in the CIF is encouraged, but should not normally include those involving H atoms; those in which three of the atoms are nearly collinear should be removed.

Crystallographic diagrams
Crystallographic diagrams will be available as part of the supplementary materials. Diagram requirements are given in x5. A labelled displacement ellipsoid diagram is normally required for each structure. Authors may supply additional figures e.g. packing diagrams. The use of colour is encouraged, but poor contrast (e.g. pale colours with a white background) should be avoided.

Chemical reaction schemes
Chemical reaction schemes or schemes showing more than one compound will be available as part of the supplementary materials. They should be supplied as supplementary figures and should have appropriate captions included in _publ_section_figure_captions (see x5.4).

Powder diffraction data
For papers that present the results of powder diffraction profile fitting or refinement (Rietveld) methods, the primary diffraction data, i.e. the numerical intensity of each measured point on the profile as a function of scattering angle, should be deposited. Papers reporting Rietveld refinements should include a supplementary figure showing the diffraction profile and the difference between the measured and calculated profiles.

Structure factors
The reflection data h, k, l, Y meas , Y meas , Y calc (where Y is I, F 2 or F) must be supplied as an electronic file in CIF format during the submission process.

Data requirements
A list of all data required for submission is available from the online CIF help page (see x8). If the submitted data are incomplete, inadequate or incorrect, the author will be informed promptly. Authors are required to pre-check each CIF (see x1.1) prior to submission. A more complete description of the data-validation checks applied to submitted CIFs is available from the online CIF help page (see x8).
Data-precision indicators will be published for all papers. Details of these can be found at http://journals.iucr.org/services/cif/ dataprecision.html.
The most important data requirements are summarized below.
_chemical_formula_moiety _chemical_formula_moiety _chemical_formula_sum _chemical_formula_sum The chemical formula must be consistent with the atomic content specified by the _atom_site_ information, and match the _chemical_formula_weight. If atoms are missing from the atomic model, the moiety and sum formulae should state the assumed overall formula.

_symmetry_space_group_name_H-M _symmetry_space_group_name_H-M
The space group must encompass the highest symmetry permitted by the diffraction intensities, and be consistent with the _cell_ length_ and _cell_angle_ values.

_cell_formula_units_Z _cell_formula_units_Z
The number of formula units in the unit cell must comply with that expected from the chemical formula, the space group and the _atom_site_ data.

_exptl_crystal_colour _exptl_crystal_colour
The crystal colour should comply with the codes listed in the online author help page (see x8).

_exptl_crystal_size_max _exptl_crystal_size_max
Authors are encouraged to use crystals no larger than the incident X-ray beam diameter, particularly when heavy or strongly absorbing elements are present in the material. For best results, the crystal should be uniformly bathed in the X-ray beam. The size of the beam at the crystal is normally determined by inter alia the nature of the X-ray source and the beam optics. Note that with fine-focus sealed X-ray tubes, the use of a collimator larger than the filament diameter does not automatically increase the size of the uniform part of the incident beam.

_exptl_absorpt_correction_type _exptl_absorpt_correction_type
Permitted absorption-type codes are listed in the online CIF help page (see x8). A type code must be accompanied by a reference to the method or the software used; this should be given in the field _exptl_absorpt_process_details. The need for absorption corrections, and the appropriate type of correction, is dependent on the value _exptl_absorpt_coefficient_mu and the crystal size values _exptl_crystal_size_min, _mid and _max. If x is the medial size _mid, the product x provides an indication of the type of correction needed. Analytical or numerical corrections may be beneficial if x exceeds 1.0 and are strongly recommended if x is above 3.0. Empirical methods based on analyses of equivalent and redundant reflections (multi-scan methods) are acceptable. Corrections are usually unnecessary if x is below 0.1. Refined absorption methods are discouraged except in special circumstances. The transmission-factor limits _exptl_absorpt_correction_T_min and _max should agree with those expected for the crystal shape and size, and . These items should refer to the complete set of measured data before any merging of symmetry-equivalent reflections, and not only to the unique set of data.

_reflns_number_total _reflns_number_total
The number of symmetry-independent reflections excludes the systematically extinct intensities. Authors are encouraged to use all symmetry-independent reflections in the refinement of the structure parameters.

_reflns_threshold_expression _reflns_threshold_expression
This threshold, which is based on multiples of I, F 2 or F, serves to identify the significantly intense reflections, the number of which is given by _reflns_number_gt. These reflections are used in the calculation of _refine_ls_R_factor_gt. The multiplier in the threshold expression should be as small as possible, typically 2 or less.

_diffrn_reflns_theta_max _diffrn_reflns_theta_max
The max of measured reflections should be such that sin max / exceeds 0.6 Å À1 (i.e. max > 25 for Mo K; max > 67 for Cu K). It is expected that all possible unique reflections out to at least the above specified minimum limits are measured. This provides the minimum number of reflections recommended for an average structural study. If intensities are consistently weak at the recommended max , low-temperature measurements may be needed unless a study at a specific temperature (or pressure) is being reported.

_diffrn_measured_fraction_theta_max _diffrn_measured_fraction_theta_max
This is the fraction of unique (symmetry-independent) reflections measured out to _diffrn_reflns_theta_max. Ideally, this should be as close to 1.0 as possible.

_diffrn_reflns_theta_full _diffrn_reflns_theta_full
When _diffrn_measured_fraction_theta_max is less than 1.0 because of some missing high-angle reflections, full is the diffractometer angle at which the measured reflection count is close to complete. The fraction of unique reflections measured out to this angle is given by _diffrn_measured_fraction_theta_full.

_diffrn_reflns_av_R_equivalents _diffrn_reflns_av_R_equivalents
Sufficient symmetry-equivalent reflections must be measured to provide a good estimate of the intensity repeatability. This is particularly important when absorption corrections are applied (this value is calculated after the corrections are applied to the intensities).

_refine_ls_R_factor_gt _refine_ls_R_factor_gt
Note that this value is not intended as a reliable gauge of structure precision, which is better determined from the standard uncertainties of the parameters (these depend on the number and reliability of the measured structure factors used in the refinement process).

_refine_ls_number_reflns _refine_ls_number_reflns
The number of reflections used in the refinement should be as large as possible, and should, if possible, be greater than the number of refined parameters _refine_ls_number_parameters by at least a factor of 10 if the structure is centrosymmetric, or by a factor of 8 if it is not.

_refine_ls_number_parameters _refine_ls_number_parameters
This is the number of coordinate, atomic displacement, scale, occupancy, constraint, restraint, extinction and other parameters refined independently in the least-squares process. It is possible, and sometimes desirable, to reduce this number by the appropriate application of geometric constraints.

_refine_ls_number_restraints _refine_ls_number_restraints
This gives the number of applied restraints. Concise details of what these restraints were should be included in the _refine_ special_details section of the CIF.

_refine_ls_hydrogen_treatment _refine_ls_hydrogen_treatment
The codes which identify the treatment of H-atom parameters are listed in the online CIF help page (see x8). Detailed text about the treatment of H-atom sites should be placed in _publ_section_ exptl_refinement. Authors should note the advice on H-atom treatment given in the SHELXL97 manual, x4.6: 'For most purposes it is preferable to calculate the hydrogen positions according to wellestablished geometrical criteria and then adopt a refinement procedure which ensures that a sensible geometry is retained'. Authors should note that H-atom sites which have been fixed or constrained by geometry will not have s.u. values associated with them.

_refine_ls_weighting_scheme _refine_ls_weighting_scheme
Weighting schemes for refinements should be based on the standard uncertainties in the measured reflection data.

_refine_ls_shift/su_max _refine_ls_shift/su_max
This is the largest ratio of the refinement shift to standard uncertainty after the final round of refinement and is typically within AE0.01 if sufficient least-squares refinement cycles have been employed. A value above AE0.05 is considered unusual and values beyond AE0.1 are a sign of incomplete refinement, unaccounted-for disorder or high correlation between parameters that should be constrained. Authors should explain the reasons for a high value in _publ_section_ exptl_refinement.

_refine_diff_density_min _refine_diff_density_min _refine_diff_density_max _refine_diff_density_max
These values are expected to be small, especially for light-atom structures. If their magnitudes are such that a validation alert is generated, the label and the distance of the closest atom site should be reported in _publ_section_exptl_refinement.

_geom_ _geom_
All geometry values must originate from the submitted _atom_ site_fract_ values. Only geometry values of significance to the structure will be published. These must be identified with a _geom_..._flag value of yes in the submitted CIF. Note that dimensions involving H-atom sites which have been fixed or constrained by geometry will not have s.u. values associated with them. Details of all bond lengths and angles involving H atoms must be included in the CIF, even if they have been constrained.

_atom_site_ _atom_site_
Atomic coordinates for molecular structures should be supplied as connected sets. Whenever structure geometry permits, it is normally expected that the set of connected coordinates which specify the asymmetric unit will lie within the basic unit cell. Values of _atom_site_occupancy should be 1.0 except for disordered or nonstoichiometric atom sites. Atom sites constrained to model disorder must be indicated by _atom_site_disorder_group. The overall packing in the structure will be checked for significant vacant regions (i.e. voids) indicating omitted solvent molecules. Note that s.u. values should not be appended to parameters which are fixed by symmetry, geometry or other constraints. In systems with hydrogen-bonded networks, it is expected that the asymmetric unit will be chosen so that the minimum number of symmetry operators is required to specify the hydrogen-bond network.

_atom_site_aniso_U_ _atom_site_aniso_U_
Checks will be made for non-positive-definite anisotropic atomic displacement parameters. The ratio of maximum to minimum eigenvalues should not, except in special circumstances (e.g. disorder), exceed 5.

_refine_ls_abs_structure_details _refine_ls_abs_structure_details
This item should describe the method applied, with a literature citation if necessary, and the number of Friedel pairs used in the determination of the absolute structure parameter (e.g. _refine_ ls_abs_structure_Flack). If the structure is non-centrosymmetric, an absolute structure parameter is expected. The reliability of this parameter increases with the number of Friedel-related intensities, and the use of a large fraction of the complete set of Friedel pairs in the refinement is strongly recommended. If the choice of X-ray wavelength means that the f 00 terms of the atomic scattering factor expressions are very small and no useful absolute structure parameter can be refined (i.e. the value of the absolute structure parameter is meaningless because of its large s.u. value), authors should consider merging the Friedel-pair reflections before final refinement. They should then report in the _publ_section_ exptl_refinement section of the CIF that they have merged Friedel pairs for the final refinement. Authors are strongly advised to consult papers by Flack & Bernardinelli which discuss the use and meaning of the Flack parameter and its s.u. value [Acta Cryst. (1999), A55, 908-915;J. Appl. Cryst. (2000), 33, 1143-1148. For pertinent comments on the determination of absolute structure authors are also referred to the papers by Jones [Acta Cryst. (1986)

Diagram requirements
A set of guidelines for preparing figures is available from http:// journals.iucr.org/j/services/help/artwork/guide.html. The chemical structure diagram (see x2.8 for a typical example) and supplementary crystallographic diagrams (see x3.5) should be prepared in HPGL, PostScript, encapsulated PostScript or TIFF format. The resolution of bitmap graphics should be a minimum of 300 d.p.i.

Supplementary crystallographic diagrams
For molecular compounds, a clear, well-presented ellipsoid plot is normally required for each independent species to show the stereochemistry and any unusual atomic displacements or disorder. For polymeric materials the displacement ellipsoid plot should show at least the chemically unique fragment; for other structures, a packing or polyhedron diagram is required. All non-H unique atom sites should be identified with labels consistent with those for the supplied atomic coordinates. Distances and angles should not be shown in the crystallographic diagram. The orientation of crystallographic figures and chemical structural diagrams should correspond as closely as possible.
Diagrams should be briefly described in the Comment section for the benefit of readers.

Submission
Diagrams should be submitted electronically via the web submission interface. All diagrams must be submitted in this way.

Lettering and symbols
Atom site labels in supplementary crystallographic diagrams should not contain parentheses and should match labels used in the atom site lists and text. The labels should not overlap or touch ellipsoids or bonds. Descriptive matter should be placed in the caption. Packing diagrams must show the cell-axis directions (labelled a, b, c) and the cell origin (labelled O).

Numbering and figure captions
A list of the figure captions should be included in _publ_ section_figure_captions. Captions of labelled displacement ellipsoid plots must state the probability limit used. If H atoms are shown by small spheres of an arbitrary size, this need not be stated in the caption.

Enhanced figures
An online tool for authors to prepare standard and corresponding three-dimensional interactive structural diagrams is available from http://submission.iucr.org/jtkt. 6. Nomenclature 6.1. Crystallographic nomenclature Authors should follow the general recommendations produced by the IUCr Commision on Crystallographic Nomenclature (see reports at http://www.iucr.org/iucr/commissions/cnom.html).
Atom sites not related by space-group symmetry should be identified by unique labels composed of a number appended to the IUPAC chemical symbol (e.g. C5, C7 etc.). Label numbers should not be placed in parentheses. Chemical and crystallographic numbering should be in agreement wherever possible. Crystallographically equivalent atoms in different asymmetric units should be identified in the text with lower-case Roman numeral superscripts appended to the original atom labels and the symmetry operators defined [e.g. C5 i ; symmetry code: (i) 1Àx, Ày, 1Àz]. In diagrams, Roman numeral notes for authors Acta Cryst. (2008). E65, e1-e8 IUCr Notes for authors e7 superscripts are preferred, but symmetry-related atoms may be marked by additional symbols or letters, with these defined in the caption. Atom labels should be as concise as possible and not contain superfluous characters, e.g. leading zeroes are unnecessary so that C01, C02 should appear as C1, C2, etc. H-atom numbers should correspond with that of their parent atom label, e.g. a phenyl H on atom C1 should appear as H1, not H1A, and methine H atoms on C1 should appear as H1A and H1B or H11 and H12, unless this leads to naming ambiguities. Chemically ambiguous labels such as HO1a (signifying an H atom attached to an O atom) should be avoided. If there are supplementary figures with packing plots in a paper, the atom labels in these plots should correspond with the asymmetricunit coordinates. Symmetry-related atoms can be marked by suffixes to the atom labels; the symmetry operations to which these refer should be defined in the figure caption.
Space groups should be designated by the Hermann-Mauguin symbols. Standard cell settings, as listed in Volume A of International Tables for Crystallography, should be used unless objective reasons to the contrary are stated. A list of equivalent positions should also be supplied. Hermann-Mauguin symbols should be used for designating point groups and molecular symmetry. If there is a choice of origin, this should be stated in _publ_section_exptl_refinement.

Nomenclature of chemical compounds
Names of chemical compounds and minerals should conform to the nomenclature rules of the International Union of Pure and Applied Chemistry (IUPAC), the International Union of Biochemistry and Molecular Biology (IUBMB), the International Mineralogical Association (IMA) and other appropriate bodies. Any accepted trivial or non-systematic name may be retained, but the corresponding systematic (IUPAC) name should also be given. For crystal structures containing chiral molecules, authors should make it clear whether the crystal structure is a racemate or enantiopure, and if enantiopure whether or not the assignment of the absolute configuration is justified. Absolute configuration should be indicated by using the CIF data item _chemical_absolute_configuration. The title, compound name, chemical diagrams, atomic coordinates and space group must correspond to the enantio-composition and the selected configuration. It is also most helpful to indicate the crystallographic and non-crystallographic symmetry of each molecule in the asymmetric unit.

Units
The International System of Units (SI) is used except that the å ngströ m (symbol Å , defined as 10 -10 m) is generally preferred to the nanometre (nm) or picometre (pm) as the appropriate unit of length.
Recommended prefixes of decimal multiples should be used rather than 'Â10 n '.

References
All references cited in the article and in the supplementary materials should be given in the reference list. An extensive list of references is inappropriate for manuscripts submitted to this journal, which is intended for short structural reports. Manuscripts giving a substantive discussion of a crystal structure and including many references are more appropriately submitted to Acta Crystallographica Section C.
Note that inclusive page numbers must be given, except when the cited article has only one page, and that all computer programs given in the relevant _computing_..._ entries must be referenced and included in the reference list. Identification of individual structures in the paper by use of database reference (identification) codes should be accompanied by a full citation of the original literature in the reference list. The CIF editor, publCIF (see x1.1), allows the consistency of references and citations to be checked.

Crystallography Journals Online
All IUCr journals are available on the web via Crystallography Journals Online; http://journals.iucr.org/. Full details of guidelines for the preparation and editing of a CIF, the data items required therein, standard data codes and keywords, CIF templates, example CIFs, and data-validation criteria and procedures can be found via the online author help page at http://journals.iucr.org/e/services/ cifinfo.html.

Example of a submission and its published version
An example CIF submission can be found at http://journals. iucr.org/services/cif/examples.html; this paper has been published in the March 2007 issue of the journal [Clegg & Martin (2007). Acta Cryst. E63, m856] to show the features of the short-format style articles.

Electronic status information
Authors may obtain information about the current status of their paper at http://journals.iucr.org/services/status.html.

Proofs
Proofs will be provided electronically as PDF files, and the correspondence author will be notified by e-mail when the proofs are ready for downloading. Any proof corrections must be returned within two days. Proofs will have been checked already by the Section Editors, who reserve the right to make minor changes for consistency and conformity to Section E standards; any remaining problems will be referred back to authors.

Reprints
After publication, the correspondence author will be able to download the electronic reprint of the published article, free of charge.

Open access
Acta Crystallographica Section E is an open-access journal. The costs of peer review, of journal production, and of online hosting and archiving will be met by charging an open-access fee to authors.
Authors will be asked to pay an open-access fee upon acceptance of their article for publication. Authors from developing countries may apply for their open-access fees to be waived. Waiver requests must be made before submission of an article to the journal.
Authors whose institution has a full subscription to Acta Crystallographica Section C are eligible for a discount on the open-access fee. In addition, discounts are available for advance payment of openaccess fees.
Full details of the open-access arrangements for Section E are available at http://journals.iucr.org/services/oa/openaccess_e.html. notes for authors e8 IUCr Notes for authors