The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACT:We describe the synthesis and characterization of a family of materials, Zr 1-x Sn x Mo 2 O 8 (0 < x < 1) whose isotropic thermal expansion coefficient can be systematically varied from negative to zero to positive values. These materials allow tunable expansion in a single phase as opposed to using a composite system. Linear thermal expansion coefficients, α l , ranging from -7.9(2) × 10 -6 K -1 to +5.9(2) × 10 -6 K -1 (12 to 500 K) can be achieved across the series; contraction and expansion limits are of the same order of magnitude as the expansion of typical ceramics. We also report the various structures and thermal expansion of "cubic" SnMo 2 O 8 , and use time-and temperature-dependent diffraction studies to describe a series of phase transitions between different ordered and disordered states of this material.

The remarkable room temperature structure of trimethyltin hydroxide comprises a total of 32 crystallographically independent SnMe3OH units arranged in four independent coordination polymer strands. We suggest that a Z′ = 4 value is more appropriate than Z′ = 32, reflecting the polymeric structure of the compound. DSC, single crystal and XRPD studies show that on cooling below ca.160 K the structure undergoes a first order phase change to a symmetric Z′ = 1 structure with just one crystallographically unique SnMe3OH unit. The phase change is reversible, and on warming past 176 K the high Z′ structure is regenerated, in an endothermic transition. The Z′ = 1 and 4 structures are an enantiotropic pair, and trimethyltin hydroxide represents a case where the higher Z′ structure is the most stable form at high temperature with the high Z′ value possibly arising from a consideration of the dynamics of the crystal as a whole.

A novel unsymmetrical dibenzylidene acetone (monothiophos-dba, compound 3), containing two chemically different alkene moieties, undergoes a selective photochemically-induced [2+2] cycloaddition solid-state transformation (single crystal and powder), as shown by X-ray diffraction methods. In the single crystal the rate constant for the cycloaddition reaction was determined {k = (2.3 ¡ 0.1) 6 10 24 s 21 }, with a 69% conversion attained, which compares well with a twophoton irradiation experiment using a Nd:YAG laser pumped dye laser at 605 nm radiation (66% conversion). Full conversion was attained using powdered 3 after 43 h. A similar conversion was noted between the single crystal and powder forms (59% and 66% conversion after 5 h irradiation). Irradiation of monothiophos-dba in solution using a 325 nm laser, and monitoring by 1 H NMR spectroscopy, showed that no cycloaddition occurred, but exclusive photochemically-induced trans A cis isomerisation of the alkene bond connecting the unsubstituted aryl group (cis A trans isomerisation in these electron-deficient and polarised CLC bonds occurs rapidly by thermal equilibration).

Samples of cubic Zr1‐xSnxMo2O8 (0.2 ≤ x ≤ 1) are prepared by coprecipitation of aqueous ZnCl4 and ZrOCl2 with (NH4)6Mo7O24 followed by a controlled heating step (853 K, 0.5 h, heating rate of 2 K/min).

(2013) 'Unexpected low temperature behaviour of piroxicam monohydrate. ', ChemPhysChem., 14 (4). pp. 675-679.Further information on publisher's website: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. MonohydrateKatharina Fucke, [a] Alison J. Edwards, [b] Michael R.Probert, [a] Sarah E. Tallentire, [a] Judith A. K. Howard, [a] and Jonathan W. Steed* [a] Pharmaceutical compounds can crystallise in different polymorphic forms with the same chemical composition; a phenomenon that has been studied for almost 200 years, [1] and remains a major issue in the pharmaceutical industry. Additional problems arise from solvated crystal forms, which incorporate one or more types of solvent from the crystallisation medium into the crystal. [2] In the special case of water incorporation, the crystal form is called a hydrate. Pharmaceutical hydrates, which can vary widely in both composition and stability, are simultaneously favoured and feared. Hydrates exhibit the lowest solubility in water of all crystal forms of a compound and hence hydrate formation can seriously influence the bioavailability and thus the safety and efficacy of a medication.[3] As a result there is considerable current interest in the study of water clusters in crystalline hydrates. [4] Hydrated crystal structures also shed light on the fundamental nature of homomeric interactions between water molecules and heteromeric interactions between water and host molecules in molecular solids. [4b, 5] With the help of modern diffraction techniques and computational studies, these interactions can now be accurately structurally characterised, [6] making essential information available for ab initio crystal structure prediction of hydrates. [7] We have focussed on the neutron structural characterisation of a range of pharmaceutically relevant hydrates. [5b, 8] As part of this study we have investigated piroxicam (PIR, Figure 1), which is a non-steroidal anti-inflammatory drug (NSAID) used in the treatment of chronic pain in rheumatoid arthritis and osteoarthritis. PIR is listed in both the European [9] and the US Pharmacopoeias, [10] and is reported to exist in three different unsolvated crystal forms, [11] a monohydrate, [12] and several multicomponent crystals and salt forms. [13] Our interest lies mainly in the interaction of water of crystallisation with the host molecule in the monohydrate structure. We now report accurate hydrogen atom positions for PIR monohydrate derived from neutron diffraction data as well as the substance's remarkable behaviou...