Cluster analyses of metal-organic fragments using the dSNAP software.

The dSNAP computer program has been used to classify searches of the Cambridge Structural Database for two ligands: -O-CH(2)-CH(2)-O- and N(CH(2)CH(2)O-)(3) commonly found in metal-organic systems. The clustering method used is based on total geometries (i.e.

Solving the crystal structures of zeolites using electron diffraction data. II. Density-building functions.

A density-building function is used to solve the crystal structures of zeolites from electron diffraction data using both two- and three-dimensional data sets. The observed data are normalized to give unitary structure factors |U(h)|(obs). An origin is defined using one to three reflections and a corresponding maximum-entropy map, q(ME)(x), is calculated in which the constraints are the amplitudes and phases of the origin-defining reflections.

Solving the crystal structures of zeolites using electron diffraction data. I. The use of potential-density histograms.

The maximum-entropy and likelihood method for solving zeolite crystal structures from electron diffraction data is modified to use potential-map-density histograms as an additional figure of merit. The experimental histogram is compared to an idealized one (based on known zeolite structures) using Pearson and Spearman correlation coefficients. These supplement the use of log-likelihood estimates as figures of merit to select the optimal solution from a collection of phase sets.

Using small molecule crystal structure data to obtain information about sulfonamide conformation.

Understanding the conformations adopted by the sulfonamide group is essential to the understanding of the way that sulfa drugs act upon the body. The relative energies of these conformations in the solid state are estimated from the Cambridge Structural Database (CSD) using cluster analysis, and are used to confirm earlier findings that many high-level ab initio calculations do not reproduce the observed solid-state structure. These conformational studies have been extended to the adjacent torsion angles, and it has been shown that the sulfonamide group significantly affects the form adopted.

Using cluster analysis to study transition-metal geometries: four-coordinate complexes with two salicylaldiminato or related ligands.

Cluster analysis is shown to be an effective method to analyse and classify metal coordination geometry in a very large number of four-coordinate bis-salicylaldimato (or bis-beta-iminoketonate) transition-metal complexes available in the Cambridge Structural Database. The methods described require no prior knowledge of chemistry to be input; retrieved structures are automatically clustered into groups based purely on the geometric similarity of the fragments and these groupings can then be interpreted by the structural chemist.

The application of cluster analysis to identify conformational preferences in enones and enimines from crystal structural data.

Cluster analysis can be an effective tool for analysing large quantities of data. Here it has been applied to the conformational analysis of enones and enimines in the crystalline solid state, using structural information mined from the Cambridge Structural Database. The forms that are common in the gaseous state and in solution are already known from spectroscopic studies.

Direct electron crystallographic determination of zeolite zonal structures.

The prospect for improving the success of ab initio zeolite structure investigations with electron diffraction data is evaluated. First of all, the quality of intensities obtained by precession electron diffraction at small hollow cone illumination angles is evaluated for seven representative materials: ITQ-1, ITQ-7, ITQ-29, ZSM-5, ZSM-10, mordenite, and MCM-68. It is clear that, for most examples, an appreciable fraction of a secondary scattering perturbation is removed by precession at small angles.

Electron crystallography of zeolites--the MWW family as a test of direct 3D structure determination.

The efficacy of direct methods for solving the crystal structures of zeolites from electron diffraction data is evaluated for a series of related materials, i.e. MCM-22, MCM-49 and ITQ-1.