Nitromalonamide has a remarkably short intramolecular hydrogen bond with an O−O distance of 2.391(3) Å, which according to some expectations would indicate a symmetric hydrogen bond. However, the enol hydrogen is confirmed by neutron diffraction to have an asymmetric position between the two oxygen atoms in the otherwise quite symmetrical molecule. The O−H distances are 1.14(1) Å and 1.31(1) Å. Analysis of the atomic displacement parameters of the enol hydrogen and comparison with those of similar systems indicate that the hydrogen atom resides in a single well potential. The experimental structure is compared to geometry optimized structures obtained from high level ab initio computations and, except for the position of the enol hydrogen, generally good agreement is obtained when correlation is taken into account. The significant differences between experimental and ab initio O−H bond lengths are ascribed to dynamical and intermolecular effects. Extremely small proton transfer barriers of 0.6 kJ/mol at the MP2/cc-pVTZ and 1.2 kJ/mol at the B3LYP/cc-pVTZ levels of theory were calculated. The enol hydrogen is found to vibrate freely between the two oxygen atoms, without the molecule passing through a well refined transition state structure. A simple model of the crystal environment explains the asymmetry of the hydrogen bond as resulting from intermolecular hydrogen bonding.

A neutron study of the crystalline complex of 1,8-bis(dimethylamino)naphthalene (DMAN) with 1,2-dichloromaleic acid (C1MH2) has been carried out at 100K using the There is a strong correlation between the neutron and X-ray temperature factors for non-H atoms and no correlation for H-atom temperature factors. According to the neutron data the involvement of a given H atom in a weak C--H...O hydrogen bond can be correlated with the ratio of equivalent temperature factors of the H and non-H atoms to which they are attached.

The Fe-O and Fe-N bond lengths at two iron sites of the mixed-valence complex [Fe(3)O(OOCC(CH(3))(3))(6)(C(5)H(5)N)(3)] show a pronounced temperature dependence; the bonds from two of the Fe atoms to the central oxygen atoms vary by more than 0.10 Å on cooling to 10 K whereas the bond from the third iron atom is essentially invariant. The variation is such that the longest Fe-O bonds at ambient temperature are the shorter ones at 10 K, with the crossover occurring at about 90 K. The bonds to the axial pyridine ligand show the opposite dependence. The variation is attributed to an equilibrium between different configurations, which interconvert through vibronic coupling, a process that involves electron transfer between the metal atoms. The position of the absorption edge for each of the iron atoms has been determined by resonance-diffraction experiments at the Fe K edge, performed at four different temperatures. At each temperature, the order of the absorption edges corresponds to that of the experimentally determined bond lengths. The crossover near 90 K is confirmed by the resonance experiments. The absorption-edge positions are related to the formal oxidation state by calibration with reference complexes of known oxidation state. The experiments demonstrate the close relation between the changes in coordination geometry and the oxidation states of the iron atoms.

was a Swiss painter, belonging to the Constructivist movement, who spent most of his life in Ibiza, Spain. Since 1930 he occupied himself with the laws of form and colour. Parallel to Escher, he discovered laws of coloured symmetry before crystallographers started working on them (more about it in [1]). After a period of experimentation with plane groups of symmetry, he moved to a more complex level of geometric abstract art by applying non-linear transformations to the plane-group patterns. His goal was to achieve a more dynamic rendition of the patterns used. My poster illustrates four different cases of this process, starting always with a plane-group pattern and showing both the application of non-linear transformations and coloured symmetry. In his more complex patterns, two of which are shown on the poster, Hinterreiter created domains of affinely or perspectively distorted motif which were further combined by means of domain boundaries or by the operations of twinning, the latter being frowned upon very much by art specialists when mentioned as one of the analytical concepts. Another means of generalization used by Hinterreiter was a careful mapping of plane-group patterns onto curvilinear nets of different kinds, mostly combined with a skilful application of principles of dichroic or polychromatic symmetry. Unlike Escher, Hinterreiter strove to achieve the aesthetic ideal of a pure abstract form [2] with its inherent symmetries. His unique, two-step approach that combines plane group patterns with the principles of coloured symmetry and nonlinear transformations, his understanding of crystallographic and non-crystallographic symmetry and a meticulous application of these principles even to the most complex patterns produced a legacy close to the heart and mind of every true crystallographer.[1] Makovicky, E. Z. Kristallogr. 1979, 150, 13 We have been synthesizing three types of cocrystals of an API flufenamic acid (non-steroidal anti-inflammatory drug) using three different coformers (nicotinamide, salicylic acid and benzoic acid). These cocrystal structures were determined from their laboratory X-ray powder diffraction data.While the flufenamic acid nicotinamide cocrystal forms infinite one-dimensional chain structure through hydrogen bonds between the API and coformer molecules, in the other two cocrystals the flufenamic acid molecule is connected with the coformer through hydrogen bonds and the pairs of molecules are stacking. Experimental and structure analysis details will be reported in this presentation.[1] Takata N., Shiraki K., Takano R. Hayashi Y. Terada K. Cryst. Growth Des., 2008, 8, 3032. Keywords: X-ray powder diffraction, ab-initio structure determination, cocrystals Increasingly we wish to obtain a much fuller understanding of materials of interest to us, beyond the standard very valuable structure determination. To do this we must use a range of crystallographic techniques and experimental conditions, often with the additional challenge that many of the most interesting samples, unfo...

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