The title complexes, [Co(C₅H₉N)₃(C₂₁H₂₁O₃P)₂]ClO₄·2CH₂Cl₂, (I), and [Co(C₅H₉N)₃(C₂₁H₂₁O₃P)₂](ClO₄)₂·2CH₂Cl₂, (II), respectively, crystallize in the hexa­gonal space group P6₃/m and the monoclinic space group P2₁/n, respectively. The cation of complex (I) has D_3h site symmetry around the Co atom and the overall symmetry is C_3h. Complex (II) is best described as having a distorted trigonal-bipyramidal coordination, with a Co site symmetry of C_s. Compounds (I) and (II) form an analogous pair of five-coordinate Co^I and Co^II complexes with the same ligands, making it possible to establish (i) if the Co site coordination for both complexes is indeed trigonal-bipyramidal, as initially assumed, and (ii) if significant structural differences occur when the oxidation state of the metal is changed.

The title compound, [Co(C₅H₉N)₄(H₂O)₂](ClO₄)₂, crystallizes in the monoclinic space group C2/m. The cation has space-group-imposed 2/m symmetry, while the perchlorate ion is disordered about a mirror plane. The two slightly non-equivalent Co—C bonds [1.900 (3) and 1.911 (3) Å] form a rectangular plane, with a C—Co—C bond angle of 86.83 (11)°, and the linear O—Co—O C₂ axis is perpendicular to this plane. The CN bond lengths are 1.141 (4) Å and the Co—CN and CN—C angles average 175.5 (4)°. The per­chlorate counter-ions are hydrogen bonded to the water mol­ecules. The title compound is the first example of four alkyl isocyanide ligands coordinating Co^II upon initial reaction of Co(ClO₄)₂·6H₂O/EtOH with alkyl isocyanide. In all other known examples, five alkyl isocyanide mol­ecules are coordinated, as in [(RNC)₅Co—Co(CNR)₅](ClO₄)₄ (R = Me, Et, CHMe₂, CH₂Ph, C₄H₉-n or C₆H₁₁) or [Co(CNC₈H₁₇-t)₅](ClO₄)₂. This complex, therefore, is unique and somewhat unexpected.

In the title compound, C₆H₇N₂O₂⁺·I₃⁻·H₂O, the triiodide anions form two-dimensional sheets along the a and c axes. These sheets are separated by the 4-nitro­anilinium cations and water mol­ecules, which form part of an extended hydrogen-bonded chain with the triiodide along the c axis, represented by the graph set C₃³(14). The second important hydrogen-bonding inter­action is between the nitro group, the water mol­ecule and the anilinium group, which forms an R₂²(6) ring and may be the reason for the deviation of the torsion angle between the benzene ring and the nitro group from 180 to 163.2 (4)°. These two strong hydrogen-bonding inter­actions also cause the benzene rings to pack off-centre from one another, with an edge-on-edge π–π stacking distance of 3.634 (6) Å and a centroid–centroid separation of 4.843 (2) Å.

In the the title compound, C₂₉H₂₆N₂O₂, two strong intra­molecular O—HN hydrogen bonds involving the hydr­oxy and imine groups generate S(6) ring motifs. The dihedral angles between the pairs of terminal benzene rings are 89.8 (2) and 87.8 (2)°.

In the title mol­ecule, C₂₉H₂₆N₂O₂, there are two strong intra­molecular O—HN hydrogen bonds involving the hydr­oxy and imine groups, forming S(6) ring motifs. The dihedral angles between adjacent phenyl rings and phenol-containing planes are 85.27 (19) and 91.38 (18)°. In the crystal structure, weak inter­molecular C—HO hydrogen bonds connect mol­ecules into a two-dimensional network.

This paper presents an analysis of the errors in lattice parameter measurements by the Bond method due to axial misalignment of the collimator and the crystal normal. These errors were considered separately in the original presentation by Bond, but primarily with the intent of reducing the errors to acceptable limits by defining the limits of misalignment. In cases where misalignment cannot be prevented, it becomes necessary to determine the error quantitatively so that corrections can be made. The analysis leads to the result that the error in lattice parameter is related to the difference, rather than the sum, of the misalignment errors considered by Bond, and a useful method of determining the error is described. The analysis is supported by measurements of the lattice parameter of copper.

Small-angle X-ray and small-angle neutron scattering measurements were carried out on a series of porous silica precursor (unsintered) bodies with different starting chemistries. The samples were prepared from mixtures containing 10 to 30 wt% colloidal silica sol and 90 to 70 wt% potassium silicate. Particle-size distributions were derived from the data using a maximum-entropy technique. Scattering data from the porous silica samples are especially suitable for such an analysis because the colloidal particles and clusters and aggregates of these particles are verified in detail to be spherical, and the scattering instrument use for this study covered the entire range of sizes in this material and was very well calibrated. It was found that the lower the amount of colloidal silica, the broader the size distribution of the silica aggregates.

The design and operation of a new small-angle X-ray scattering instrument, optimized for high throughput at a synchrotron source, high angular and wavelength resolution, large sample cross-sectional area, accurate energy tuning, excellent signal-to-noise ratio and harmonic rejection are presented. The principles of design and implementation are given, as are the details of primary calibration of absolute intensity and experimental desmearing. The instrument has been tested for application to anomalous-scattering measurements near the chromium K edge. Preliminary results on samples of a heat-treated steel are presented as a demonstration of the capability of this experiment to separate the microstructure evolution as a function of temperature of a chromium-rich precipitate from the thermal behavior of other precipitates in the steel.

The crystal structure of the penta­cylic triterpenoid β-amyrin benzoate, C₃₇H₅₄O₂, is reported at 173 K. Short intra­molecular C—HO contacts are observed.