Abstract-From steric considerations as well as from an analysis of CD spectra a (P)-screw configuration could be attributed to the (-)-rotating molecules of poly(t-butyl isocyanide).

A method is presented for the semi‐automatic indexing of the Laue diffraction pattern. The method is based on the recognition of conics in the Laue pattern by a plane‐search algorithm in reciprocal space, after which possible cells are constructed in direct space and relative cell parameters and crystal orientation are obtained. These cells, scaled to an arbitrary volume, are refined, reduced and grouped in order of frequency of occurrence. Usually, the cell that occurs most frequently is the correct one. Other cells found have one or more axes doubled. Such cells are easily discriminated by comparison of the corresponding simulated Laue pattern with the measured one. The method is tested with different data sets of an organic and an organometallic compound collected with an image plate using white radiation of a molybdenum sealed tube. For each pattern, the correct cell was found. Further refinement of the relative cell parameters by matching of the calculated and observed positions of the Lane spots showed good agreement with the relative cell parameters obtained from monochromatic data. To scale the cells, additional information is needed. This paper demonstrates the use of the Mo emission line Kβ1 to determine the cell volume within 1.2%.

General strategies are described to obtain crystals of low-molecular-weight compounds suitable for X-ray structure determination. A survey is given of a variety of crystallization techniques together with their advantages and drawbacks, illustrated by experiences with notoriously crystallization-resisting compounds. The methods discussed range from preliminary investigations using evaporation, batch crystallization and liquid-liquid diffusion methods, via the most frequently used methods such as sitting-drop vaporphase diffusion and change of temperature, to methods such as gel crystallization, sublimation and solidification. The most successful method appears to be the sitting-drop vapor-phase diffusion. Complete crystallization routes are described, taking into account the results of preliminary investigations. The hard-to-crystallize vecuronium bromide is presented as a case study.

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