Molecular trapping by flexible coordination polymers with latent porosity

Adsorption of gases and vapours, and solid-state reactions, involving crystalline materials are areas of considerable interest. Crystalline materials can thereby be engaged in catalysis, energy storage, separation and sensing applications. The study of such behaviour often requires the application of crystallography combined with other experimental (and computational) methods to obtain a complete understanding. In this presentation, related families of coordination polymers will be discussed. The materials exhibit flexibility in the crystalline state and have been shown to reversibly absorb a variety of small molecules from the vapour phase, including alcohols and arenes, as well as gases.[1,2] The trapped molecules can be located crystallographically within the crystals and have been shown to bind either covalently, through metal-ligand bond insertion reactions, or non-covalently. A series of studies will be described, including reversible single-crystal-to-single-crystal reactions, in situ powder diffraction and spectroscopic studies. The studies involve both laboratory and synchrotron diffraction studies.

Crystal wafer as a wavelength monitor

For accurate synchrotron data collection it is important to know the precise X-ray wavelength and to be able to monitor this value. Due to the high heat load on the X-ray optics from modern sources significant drifts may occur. Any change in wavelength is reflected as a change in the unit cell parameters derived from the data and this is especially problematic for measurements of strain. A conceptually simple device has been developed to allow measurements and monitoring of the X-ray wavelength by measuring the transmission of a silicon single crystal wafer in transmission. As the crystal is rotated in the beam different hkl reflections are diffracted leading to a loss of intensity in the transmitted beam. By measuring the incident and transmitted intensity the angles of all of these peaks can be measured with high precision while rotating the crystal, with a setup rather similar to a conventional EXAFS experiment. A similar device has also recently been developed for polychromatic experiments [1]. For high energy X-rays the wafer can be left in the beam throughout the experiment and individual reflections can be scanned to monitor the wavelength as a function of time. The rich diffraction pattern which can be recorded in this geometry should contain a wealth of information as all single rocking curves are measured with high resolution on an absolute scale in comparison to the crystal absorption. The figure shows an example scan collected at 42 keV using a silicon wafer.