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|Title:||ALS/CXRO Seminar: ""Non-ambient chemical crystallography: Investigating the relationship between molecular structure and function using small molecules"|
|When:||07/11/2013 1:00 PM - 2:00 PM|
|Description:||"Non-ambient chemical crystallography: Investigating the relationship between molecular structure and function using small molecules"|
by Christopher Woodall
Non-ambient X-ray crystallography, involving the study of crystalline materials under variable temperature or pressure conditions, or under irradiation by electromagnetic radiation has undergone rapid developments in recent years thanks to increased access to synchrotron radiation, better lab sources, more versatile detectors, and improved sample environments to yield new insights into the relationship between molecular structure, properties and function.
In this presentation I will describe some of the non-ambient crystallographic and spectroscopic studies that I have carried out and present three case histories. The first describes the evolution of fascinating negative linear compressibility (NLC) when single crystals of the “rod” shaped molecule [((C6F5)Au)2(-1,4,diisocyanobenzene)] are placed under pressures from ambient to 5 GPa. The mechanism for the NLC process is elucidated using single crystal X-ray diffraction. In the second study, high pressure and variable temperature single crystal X-ray and spectroscopic techniques are used to tune the luminescence in a series of trimeric gold(I) pyrazolate complexes, by altering the intermolecular Au…Au aurophilic interactions. As part of this study, it was found that one of the materials undergoes five phase changes over the pressure range from ambient to 3.5 GPa, including an unprecedented re-entrant phase transition in a molecular system. Finally, the solvochromic properties of a platinum(II) cyanide complex, supported by a tridentate pincer ligand, with water, methanol, ethanol and acetonitrile. The complex undergoes rapid colour changes on exposure to minimum quantities of the solvents when in the solid-state. The mechanism for this process has been elucidated through a combination of crystallographic and spectroscopic studies, and the key factors have been shown to be the intermolecular Pt…Pt distances, and the dimensions of channels through the structures. It is the variation in the hydrogen bonding between the different solvents and the cyanide group that facilitates the control of the colour of the complexes.
The importance of a multi-dimensional approach, combining crystallography and spectroscopy, underpinned by quantum chemical calculations, to obtain a complete understanding of the structure and dynamics of the systems studied, is emphasised.