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In the asymmetric unit of the crystal structure of nicotinamide-succinic acid (2/1), 2C(6)H(6)N(2)O x C(4)H(6)O(4), there are two independent nicotinamide molecules in general positions and two half succinic acid molecules which lie about inversion centres. The structure contains acid-pyridine and amide-amide synthons with nicotinamide molecules forming ladders of alternating R(2)(2)(8) and R(4)(2)(8) rings linked through succinic acid to generate a corrugated hydrogen-bonded sheet. This sheet is a common supramolecular unit found in other 2:1 nicotinamide-dicarboxylic acid cocrystals, but the presence of two crystallographically distinct nicotinamides with anti and syn conformations, forming two distinct sheets within the same structure, is a novel packing feature in this type of material.

1,1'-Divinyl ferrocene (2) reacts with K(3)[Fe(CN)(6)] under basic biphasic conditions to give a [4]ferrocenophane (4) in good yield. Incorporating deuterium labels into the internal positions of the vinyl groups of 2 affects the chemoselectivity of the reaction; thus under identical reaction conditions, [D(2)]-2 reacts to provide a diol-functionalised [4]ferrocenophane, [D(2)]-D/L-6 in addition to the expected keto-alcohol, [D(1)]-4. Variants on this one-electron oxidative cyclisation methodology can be used to give other [4]ferrocenophanes; thus, the reaction of 2 with CuCl(2) in MeOH or iPrOH leads to dialkoxy [4]ferrocenophanes 19 and 20, respectively, whereas the reaction of 2 with benzyl carbamate in the presence of tBuOCl gives a bis(carbamate)[4]ferrocenophane, 21. Mechanisms to account for the formation of the products, the stereoselectivity, and the unusual isotope-dependent chemoselectivity in the reaction of 2 and [D(2)]-2 with K(3)[Fe(CN)(6)] are proposed.

The principles of social and biological evolution have been combined in a Cultural Differential Evolution hybrid global optimization technique and applied to crystal structure solution.

The crystal structures of triethyl-1,3,5-triazine-2,4,6-tricarboxylate (I), triethyl-1,3,5-benzenetricarboxylate (II) and tris-2-hydroxyethyl isocyanurate (III) have been determined from conventional laboratory X-ray powder diffraction data using the differential evolution structure solution technique. The determination of these structures presented an unexpectedly wide variation in levels of difficulty, with only the determination of (III) being without complication. In the case of (I) structure solution resulted in a Rietveld refinement profile that was not ideal, but was subsequently rationalized by single-crystal diffraction as resulting from disorder. Refinement of structure (II) showed significant variation in side-chain conformation from the initial powder structure solution. Further investigation showed that the structure solution optimization had indeed been successful, and that preferred orientation had a dramatic effect on the structure-solution R-factor search surface. Despite the presence of identical side chains in (I) and (II), only the triazine-based system retains threefold molecular symmetry in the crystal structure. The lack of use of the heterocyclic N atom as a hydrogen-bond acceptor in this structure results in the formation of a similar non-centrosymmetric network to the benzene-based structure, but with overall three-dimensional centrosymmetry. The hydrogen-bonded layer structure of (III) is similar to that of other isocyanurate-based structures of this type.

A new calcium phosphate cement is reported, which sets to form a matrix consisting of brushite, dicalcium pyrophosphate dihydrate and an amorphous phase following the mixture of beta-tricalcium phosphate with an aqueous pyrophosphoric acid solution. This reactant combination set within a clinically relevant time-frame (approximately 10 min) and exhibited a higher compressive strength (25 MPa) than previously reported brushite cements. The in vitro degradation of the beta-tricalcium phosphate-pyrophosphoric acid cement was tested in both phosphate buffered saline and bovine serum. The pyrophosphate ion containing cement reported here was found not to be hydrolysed to form hydroxyapatite in vitro like beta-tricalcium phosphate-orthophosphoric acid solution cements. This finding is significant since the formation of hydroxyapatite by hydrolysis is thought to retard in vivo degradation of brushite cements. When aged in bovine serum, the cement lost considerably more mass than when aged in phosphate buffered saline, indicating that proteins, most likely phosphatase enzymes played an important role in the degradation. As pyrophosphate ions are thought to be the source of orthophosphate ions during bone mineralisation, this new class of bone cement offers a route to new degradable synthetic bone grafting materials.

The bulk properties of organic crystalline materials depend on their molecular and crystal structures but, as many of these materials cannot be prepared in a suitable form for conventional single-crystal diffraction studies, structural characterization and rationalization of these properties must be obtained from powder diffraction data. The recent development of direct-space structure solution methods has enabled the study of a wide range of organic materials using powder diffraction data, many of structural complexity only made tractable by these advances in methodology. These direct-space methods are based on a number of global optimization techniques including Monte Carlo, simulated annealing, genetic algorithm and differential evolution approaches. In this article, the implementation and relative efficiency and reliability of these methods are discussed, and their impact on the structural study of organic materials is illustrated by examples of polymorphic systems, pharmaceutical, pigment and polypeptide structures and compounds used in the study of intermolecular networks.

A simultaneous experimental and computational search for polymorphs of chlorothalonil (2,4,5,6-tetrachloro-1,3-benzenedicarbonitrile) has been conducted, leading to the first characterization of forms 2 and 3. The crystal structure prediction study, using a specifically developed anisotropic atom-atom potential for chlorothalonil, gave as the global minimum in the lattice energy a structure that was readily refined against powder diffraction data to the known form 1 (P2(1)/a). The structure of form 2 was solved and refined from powder diffraction data, giving a disordered structure in the Rm (166) space group (Z = 3). It could also be refined against a P1 ordered model, starting from a low-energy hypothetical sheet structure found in the computational search. This shows that the disorder could be associated with the stacking of ordered sheets. The disordered structure for form 2 was later confirmed by single-crystal X-ray diffraction. The structure of form 3, determined from single-crystal diffraction, contains three independent molecules in the asymmetric unit in P2(1) (4) (Z = 6). Powder diffraction showed that this single-herringbone structure was similar to two low-energy structures found in the search. Further analysis confirmed that form 3 has a similar lattice energy and contains elements from both these predicted structures, which can be considered as good approximations to the form 3 structure.

The structures of three substituted arenesulfonamides have been solved from laboratory X-ray powder diffraction data, using a new direct-space structure solution method based on a differential evolution algorithm, and refined by the Rietveld method. In 2-toluenesulfonamide, C(7)H(9)NO(2)S (I) (tetragonal I4(1)/a, Z = 16), the molecules are linked by N-H...O=S hydrogen bonds into a three-dimensional framework. In 3-nitrobenzenesulfonamide, C(6)H(6)N(2)O(4)S (II) (monoclinic P2(1), Z = 2), N-H...O=S hydrogen bonds produce molecular ladders, which are linked into sheets by C-H...O=S hydrogen bonds: the nitro group does not participate in the hydrogen bonding. Molecules of 4-nitrobenzenesulfonamide, C(6)H(6)N(2)O(4)S (III) (monoclinic P2(1)/n, Z = 4), are linked into sheets by four types of hydrogen bond, N-H...O=S, N-H...O(nitro), C-H...O=S and C-H...O(nitro), and the sheets are weakly linked by aromatic pi...pi stacking interactions.

The crystal structure of a previously unknown triclinic polymorph of adipamide has been solved from laboratory X-ray powder diffraction data using a new direct space global optimisation method based on differential evolution.

Many crystalline solids cannot be prepared in the form of single crystals of sufficient size and/or quality for investigation using single-crystal X-ray diffraction techniques, and the opportunity to carry out structure determination using powder diffraction data is therefore essential to understand the structural properties of such materials. Although the refinement stage of the structure determination process can be carried out fairly routinely from powder diffraction data using the Rietveld profile refinement technique, solving crystal structures directly from powder data is associated with several intrinsic difficulties. Nevertheless, substantial progress has been made in recent years in the scope and potential of techniques in this field. This article aims to highlight the types of structural problems for which structure determination may now be tackled directly from powder diffraction data, and contemporary applications across several chemical disciplines are presented. A brief survey of the underlying methodologies is given, with some emphasis on recently developed techniques for carrying out the structure-solution stage of the structure-determination process.

Zn(O3PCH2OH) (1) has been formed by reaction of zinc acetate with diethyl hydroxymethylphosphonate. The acidity of the zinc solution effects hydrolysis of the phosphonate to produce phosphonic acid in situ. 1 crystallizes in the trigonal spacegroup R3, with a = 15.9701(2) A, c = 7.783(2) A, and Z = 18. The compound has channels in the [001] direction, formed by phosphonate groups bridging the octahedral coordinated zinc atoms. The zinc atoms are coordinated by the three oxygens of the phosphonate group and the oxygen of the hydroxy group.

The crystal structure of 2,4,6-triisopropylbenzenesulfonamide, C(15)H(25)NO(2)S, has been solved from X-ray powder diffraction data collected at 120 (1) K using synchrotron radiation and refined by Rietveld methods. The structure was solved by the application of a Monte Carlo method in which trial structures were generated by random movement of the molecule in the unit cell and assessed using a full-profile-fitting technique. Intramolecular flexibility was introduced into the structure solution in the form of four independent asymmetric rotors, allowing the isopropyl and sulfonamide groups to rotate freely within the molecule. The structure is monoclinic P2(1)/c, a = 16.9600 (6), b = 8.1382 (2), c = 11.7810 (2) Å, beta = 104.777 (2) degrees with Z = 4. The molecules are linked by N-H.O hydrogen bonds, with N.O distances of 2.77 (1) and 2.92 (1) Å, into two-dimensional sheets built from R(2)(2)(8) and R(6)(6)(20) rings.

Using two dimorphic species with diallelic incompatibility, Primula farinosa L. and Armeria maritima (Miller) Willd., we tested the hypothesis that an association of seedling performance with seed size, and an inverse association of seed size with seed number, might, contrary to most fitness models, select for plants which set relatively few seeds. In P. farinosa we discovered positive relationships between seed number per capsule and capsule number per inflorescence. As capsules are formed in most flowers, scapes with few flowers set the fewest seeds per capsule. This suggests that conspicuousness to pollinators and/or plant resource play an important role in reproductive success in this species. Seed size and seedling performance were also positively associated. For P. farinosa, which has multi-seeded fruits, we discovered an inverse association between seed size and seed number for capsules containing more than 65 seeds. We suggest that stabilizing selection may occur for flower number per inflorescence in this species, as inflorescences with 8-11 capsules tend to set many seeds which may be inefficiently small. This tends to confirm our hypothesis. However, for A. maritima there is a positive association between seed size and seed number per inflorescence. For such plants with single-seeded fruits there should be directional selection for large flower number pet-inflorescence, a trend which may have led to the evolution of the capitulum.