The WinGX suite provides a complete set of programs for the treatment of small-molecule single-crystal diffraction data, from data reduction and processing, structure solution, model refinement and visualization, and metric analysis of molecular geometry and crystal packing, to final report preparation in the form of a CIF. It includes several well known pieces of software and provides a repository for programs when the original authors no longer wish to, or are unable to, maintain them. It also provides menu items to execute external software, such as the SIR and SHELX suites of programs. The program ORTEP for Windows provides a graphical user interface (GUI) for the classic ORTEP program, which is the original software for the illustration of anisotropic displacement ellipsoids. The GUI code provides input capabilities for a wide variety of file formats, and extra functionality such as geometry calculations and ray-traced outputs. The programs WinGX and ORTEP for Windows have been distributed over the internet for about 15 years, and this article describes some of the more modern features of the programs.

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WinGX and ORTEP for Windows: an update

SUPERFLIP is a computer program that can solve crystal structures from diffraction data using the recently developed charge-flipping algorithm. It can solve periodic structures, incommensurately modulated structures and quasicrystals from X-ray and neutron diffraction data. Structure solution from powder diffraction data is supported by combining the charge-flipping algorithm with a histogram-matching procedure. SUPERFLIP is written in Fortran90 and is distributed as a source code and as precompiled binaries. It has been successfully compiled and tested on a variety of operating systems.

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SUPERFLIP– a computer program for the solution of crystal structures by charge flipping in arbitrary dimensions

1. Advantages of Chemical Redox Agents 878 2. Disadvantages of Chemical Redox Agents 879 C. Potentials in Nonaqueous Solvents 879 D. Reversible vs Irreversible ET Reagents 879 E. Categorization of Reagent Strength 881 II. Oxidants 881 A. Inorganic 881 1. Metal and Metal Complex Oxidants 881 2. Main Group Oxidants 887 B. Organic 891 1. Radical Cations 891 2. Carbocations 893 3. Cyanocarbons and Related Electron-Rich Compounds 894

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Chemical Redox Agents for Organometallic Chemistry

The completion of a crystal structure determination is often hampered by the presence of embedded solvent molecules or ions that are seriously disordered. Their contribution to the calculated structure factors in the least-squares refinement of a crystal structure has to be included in some way. Traditionally, an atomistic solvent disorder model is attempted. Such an approach is generally to be preferred, but it does not always lead to a satisfactory result and may even be impossible in cases where channels in the structure are filled with continuous electron density. This paper documents the SQUEEZE method as an alternative means of addressing the solvent disorder issue. It conveniently interfaces with the 2014 version of the least-squares refinement program SHELXL [Sheldrick (2015). Acta Cryst. C71. In the press] and other refinement programs that accept externally provided fixed contributions to the calculated structure factors. The PLATON SQUEEZE tool calculates the solvent contribution to the structure factors by back-Fourier transformation of the electron density found in the solvent-accessible region of a phase-optimized difference electron-density map. The actual least-squares structure refinement is delegated to, for example, SHELXL. The current versions of PLATON SQUEEZE and SHELXL now address several of the unnecessary complications with the earlier implementation of the SQUEEZE procedure that were a necessity because least-squares refinement with the now superseded SHELXL97 program did not allow for the input of fixed externally provided contributions to the structure-factor calculation. It is no longer necessary to subtract the solvent contribution temporarily from the observed intensities to be able to use SHELXL for the least-squares refinement, since that program now accepts the solvent contribution from an external file (.fab file) if the ABIN instruction is used. In addition, many twinned structures containing disordered solvents are now also treatable by SQUEEZE. The details of a SQUEEZE calculation are now automatically included in the CIF archive file, along with the unmerged reflection data. The current implementation of the SQUEEZE procedure is described, and discussed and illustrated with three examples. Two of them are based on the reflection data of published structures and one on synthetic reflection data generated for a published structure.

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PLATON SQUEEZE: a tool for the calculation of the disordered solvent contribution to the calculated structure factors

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The Halogen Bond

The determination of small-molecule structures from single-crystal X-ray data is being carried out by researchers with little or no crys- tallographic training. At the same time, completely automatic crystal structure analysis can still only be achieved under very favourable conditions. Many of the problems that cause automatic systems to fail could be resolved with suitable chemical insight, and until this is built- in, programs continue to need human guidance. CRYSTALS version 12 contains a modern crystallographic human-interface design, and novel strategies incorporating chemical knowledge and sensible crystallographic guidance into crystal structure analysis software.

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CRYSTALS version 12: software for guided crystal structure analysis

The compounds [TiCl3(dmpe)R](R = Me, CH2D, or Et; dmpe = Me2PCH2CH2PMe2) have been prepared. An X-ray crystal structure determination of [TiCl3(dmpe)Et] shows that the Ti–C–C angle of the Ti–Et moiety is 86.3(6)°. Variable-temperature n.m.r. studies show the molecule to be fluxional at room temperature. At –90 °C the n.m.r. spectra correspond to the structure found in the crystal and J(C–H) for the ethyl CH2 hydrogens is 150.2 Hz. It is concluded that the ethyl group is bonded by a [graphic omitted] system. The crystal structure of [TiCl3(dmpe)Me] has been determined from X-ray and neutron diffraction data. The data show the methyl group to be distorted such that it is tilted with respect to the Ti–C vector and one hydrogen atom closely approaches the Ti centre giving an angle for Ti–C–H of 93.5(2)°(neutron data). Variabletemperature n.m.r. studies show that [TiCl3(dmpe)R](R = CH3 or CH2D) are fluxional but provide no evidence for differentiation of the C–H moiety of the methyl group.

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Evidence for carbon–hydrogen–titanium interactions: synthesis and crystal structures of the agostic alkyls [TiCl3(Me2PCH2CH2PMe2)R](R = Et or Me)

Gypsum Overgrowths Passivate Calcite to Acid Attack

A program which utilizes the techniques of Artificial Intelligence and Expert Systems to solve problems in the area of Conformational Analysis is described. The program searches conformational space in a systematic fashion, based on the technique known as heuristic state-space search. The program proceeds by recognizing conformational units, assigning one or more conformational templates to each unit, and joining them to form conformational suggestions. These suggestions are criticized to discover logical inconsistencies, and any resulting stresses are resolved. The resulting conformational suggestions are sometimes accurate enough for immediate use, or may be further refined by a numerical program. The latter combination is shown to be quite efficient compared to purely numerical conformational search techniques.

WIZARD: AI in conformational analysis.

A method for synthesising open-framework phosphates under less-severe conditions than those employed in conventional solvothermal processes is described. Two new layered aluminum phosphates contain...

Keith Prout

Papers

CRYSTALS version 12: software for guided crystal structure analysis

Evidence for carbon–hydrogen–titanium interactions: synthesis and crystal structures of the agostic alkyls [TiCl3(Me2PCH2CH2PMe2)R](R = Et or Me)

Gypsum Overgrowths Passivate Calcite to Acid Attack

WIZARD: AI in conformational analysis.

Ambient-temperature synthesis of new layered AlPOs and GaPOs in silica gels