Single-crystal diffraction data have been recorded for a very small crystal of dimensions 8 x 18 × 175 ~rn 3. From these data the structure of piperazine silicate (EU 19) has been determined and refined to R = 0.094 for 490 observed reflections. Data collection for such a crystal has been made practicable by the high intensity of the Daresbury Synchrotron Radiation Source and the Enraf-Nonius FAST area detector diffractometer. The potential of this synchrotron radiation method for other small crystals including proteins is discussed.

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A technique is described for the milligram-scale synthesis of zeolitic molecular sieves in sealed capillary tubes. The method is ideally suited to the measurement of the linear growth rates of individual crystals. Spectroscopic characterisation of individual crystals within the sealed capillaries has been demonstrated. Detailed results for growth rates as a function of synthesis temperature and composition are presented for the isostructural zeolite ZSM-5 and silica molecular sieve silicalite (MFI framework). Length growth rates follow the Arrhenius law over a wide temperature range and have an apparent activation energy of 80 f 3 kJ mol-I. Width growth rates show more complex behaviour and yield apparent activation energies in the range 62-81 kJ mol-I, depending upon the temperature range chosen and the synthesis conditions. The crystal aspect ratio is found to increase with increasing temperature and also when the crystals are growing under chemical constraint. The maximum value observed for the length growth rate (0.5 dl/dt = (1.9-2.0) x lo-* pm h-If at 368 K agrees well with that found in earlier studies, and it is suggested that this represents a rate limit dependent upon the integration of growth species into the crystal surface. Addition of aluminium compounds, tetramethylammonium salts or ethanol reduces the growth rate, and a number of possible mechanisms are suggested. Some observations have also been made on zeolites EU-1 (EUO), ZSM-39 (MTN) and ZSM-48.

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