Structure determination of molecular materials from powder diffraction data

Current Opinion in Solid State and Materials Science 6 (2002) 125–130

Structure determination of molecular materials from powder diffraction data Kenneth D.M. Harris* School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2 TT, UK

Abstract Many solids can be prepared only as microcrystalline powders and are not suitable for structural characterization by single crystal diffraction techniques. In such cases, it is necessary to carry out structure determination using powder diffraction data. There has been considerable recent interest in this field, and considerable progress has been achieved both in the development of new techniques and in the application of these techniques to tackle a wide range of structural problems. This article highlights recent developments of techniques in this field, and their application in the field of molecular solid state chemistry.  2002 Elsevier Science Ltd. All rights reserved. Keywords: Structure determination; Molecular materials; Powder diffraction

1. Introduction Although single crystal X-ray diffraction is the most powerful and routinely applied technique for determining crystal structures, an intrinsic limitation of this technique is the requirement to prepare a crystal of sufficient size, quality and stability. When appropriate single crystals cannot be obtained, it is necessary instead to tackle structure determination using powder diffraction data. Crystal structure determination from diffraction data (single crystal or powder data) comprises the following stages: (i) unit cell determination (‘indexing’) and symmetry determination (space group assignment), (ii) structure solution, and (iii) structure refinement. Determination of the unit cell requires consideration of the positions of peaks in the powder diffraction pattern, whereas space group assignment, structure solution and structure refinement also require consideration of the relative intensities of the peaks. Structure solution starts from no knowledge of the arrangement of atoms or molecules within the unit cell, and aims to derive a good approximation to the crystal structure from analysis of the experimental diffraction data. If a sufficiently good structure solution is obtained, a high quality structure may then be obtained by refinement of this structural model in the structure refinement stage. For powder diffraction data, refinement of crystal struc*Tel.: 144-121-414-7474; fax: 144-121-414-7473. E-mail address: [email protected] (K.D.M. Harris).

tures can be carried out fairly routinely using the Rietveld refinement technique. In general, however, structure solution from powder diffraction data is a significantly greater challenge than structure refinement, and consequently, the main emphasis of fundamental developments in recent years has focused on the structure solution stage of the structure determination process. There are two general strategies for structure solution from powder diffraction data—the ‘traditional’ approach and the ‘direct-space’ approach. In the traditional approach, the aim is to extract the intensities I(hkl) of individual reflections directly from the experimental powder diffraction pattern, and then to use these I(hkl) data in the types of structure solution calculation that have been developed for single crystal diffraction data (for example, direct methods and Patterson methods). However, as a consequence of peak overlap in the powder diffraction pattern, it is often difficult to obtain reliable values of the intensities I(hkl) of the individual diffraction maxima from the experimental powder diffraction pattern, and much fundamental work on the development of the traditional approach has been devoted to improving the reliability of the procedures for peak extraction. In the direct-space approach, trial structures are generated in direct space, independently of the experimental powder diffraction data, and the suitability of each trial structure is assessed by comparing the powder diffraction pattern calculated for the trial structure and the experimental powder diffraction pattern. This comparison is quantified using an appropriate R-factor (often the weighted

1359-0286 / 02 / $ – see front matter  2002 Elsevier Science Ltd. All rights reserved. PII: S1359-0286( 02 )00045-1

126

K.D.M. Harris / Current Opinion in Solid State and Materials Science 6 (2002) 125–130

powder profile R-factor R wp is used, as in Rietveld refinement). The direct-space strategy for structure solution aims to find the trial crystal structure that has the lowest possible R-factor, and the approach is equivalent to exploring a hypersurface R(G ) to find the global minimum on the hypersurface, where G represents the set of variables that defines the structure. In principle, any technique for global optimization (e.g., Monte Carlo, simulated annealing, genetic algorithms, etc.) may be used to locate the lowest point on the R(G ) hypersurface, and a wide variety of different global optimization strategies have been employed in this regard. The field of structure determination from powder diffraction data has experienced a period of considerable development in recent years, and the aim of this article is to survey the developments and progress published in the literature during 2001 and the early part of 2002. The article is focused on applications of such techniques in the specific case of molecular crystal structures, although the developments of fundamentals and methodology described in this article clearly have much wider applicability to other classes of materials. In continuation of recent trends, the majority of applications of powder diffraction techniques to determine the structures of molecular crystals have employed direct-space techniques for structure solution, although some examples employing traditional techniques have also been reported. The article gives emphasis to those applications involving complete structure determination from powder diffraction data, as opposed to cases in which structural models have been obtained from other sources and then refined using powder diffraction data. Furthermore, with regard to fundamental aspects of the development of methodology, focus is given to developments of structure solution techniques, partly in recognition of the fact that this remains, in general, the most challenging stage of the structure determination process. There have been a number of review articles on structure determination from powder diffraction data, including two comprehensive reviews [1,2] covering essentially all aspects of the field, as well as a number of shorter reviews [3,4] of a general nature. Other review articles have tended to focus on the work of specific research groups, covering the development of direct-space methodology [5], the combination of Monte-Carlo / simulated annealing techniques with first principles density functional theory calculations [6], the use of a grid-search technique [7], applications of genetic algorithm methods [8,9], a simulated annealing approach [10], and a Monte Carlo program [11].

2. Fundamentals As discussed above, fundamental developments of methodology have mainly concerned the structure solution stage of the structure determination process.

Developments within the domain of the traditional approach for structure solution have included a method [12] for pattern decomposition (i.e., the extraction of the intensities of individual reflections from the powder diffraction pattern) based on utilising preferred orientation in textured samples. Improved procedures for extraction of accurate integrated intensities from overlapped reflections, implemented within the EXPO program, have been described [13] and are shown to reduce the phase error in the phasing process of direct methods structure solution calculations. The EXPO program has also been extended [14] to include the implementation of real-space techniques for phase extension and refinement, as applied previously to structure solution of protein structures. Clearly this strategy introduces aspects of direct-space information within the framework of a traditional structure solution approach. Another development in the same general direction concerns the use of direct-space information to assist in the assignment of peaks in electron density maps produced from direct methods structure solution calculations [15]. An interesting development, with potentially wide applicability, concerns the use of structure envelopes in structure solution from powder diffraction data [16]. The structure envelope essentially defines regions of high electron density in the structure, and can be estimated by considering a small number of strong low-angle reflections in the powder diffraction pattern. Structure envelopes have been used in structure solution of a number of examples, including a tri-b-peptide. In this case, a simulated annealing program was used to locate the correct position of the molecule within the structure envelope. Clearly the use of structure envelopes in this manner can serve to reduce significantly the amount of structural space that requires to be explored in direct-space structure solution calculations. Within direct-space techniques, one factor that can aid future progress is to be able to visualise and understand the multi-dimensional R-factor hypersurfaces that are explored using such techniques. In this regard, a method for determining general sections through such hypersurfaces has been described [17], in which the values of all the variables that define the hypersurface are allowed to vary simultaneously. New methods have also been developed [18] for analysing the evolutionary events that occur during genetic algorithm structure solution calculations, including methods for probing the R-factor distribution within the population and for analysis of the evolutionary trajectory that leads to the correct structure solution. This method allows an understanding of the specific evolutionary events that are important in progressing towards the correct structure solution, and may clearly be exploited in the further development of the genetic algorithm methodology. A detailed analysis of simulated annealing strategies, applied in the field of structure determination from diffraction data (single crystal or powder), has been described

K.D.M. Harris / Current Opinion in Solid State and Materials Science 6 (2002) 125–130

[19]. The findings in this paper provide important new aspects of fundamental understanding, which may lead towards improvements in direct-space methods for structure solution based on simulated annealing strategies. In another development of direct-space methodology, a technique based on a differential evolution strategy has been described [20], and has been applied successfully to solve the structure of a triclinic polymorph of adipamide. Other fundamental developments have included an approach, based on probability theory, for determination of space group from powder diffraction data [21], and a modified Rietveld refinement procedure, developed within the context of Bayesian probability theory, that is shown to be robust even when the powder diffraction data contains peaks due to impurity phases [22].

3. Applications Techniques for structure determination of molecular materials from powder diffraction data have been applied to a broad range of examples from different areas of structural science, and have involved the application of each of the strategies for structure solution described above. In some cases, combinations of different techniques have been employed, involving either the use of different structure solution strategies, or the use of structure solution techniques in tandem with other sources of information (e.g., energy calculations or spectroscopic information). The traditional approach for structure solution has been applied in a number of cases, including the structure determination of 3,5-diisopropyl-4-nitropyrazole by employing a Patterson search method [23]. Direct methods, on the other hand, have been employed in structure determination of norbornene [24] and R-thiocamphor [25]. In an interesting series of papers, traditional techniques and direct-space techniques have been used in combination, by using a direct-space calculation (Monte Carlo method) to locate ‘missing atoms’ in electron density maps produced from structure solution calculations using a traditional approach (direct methods). This strategy has been applied in the structure determination of 2,2dihydroxymethylbutanoic acid [26], for which two oxygen and five carbon atoms were found by direct methods and the positions of the remaining two oxygen and one carbon atoms in the structure were found subsequently by the Monte Carlo calculation. This strategy has also been applied to find calcium atoms and water molecules in a zeolitic material [27], and to find missing atoms in the partially solved structures of a-SiO 2 and Mg 2 SiO 4 [28]. The genetic algorithm technique for structure solution has been applied in a number of cases, including structure determination of 4,49-trimethylenedipyridine [29], 2(methylsulfonyl)ethyl succinimidyl carbonate [30] and 2,5bis(trimethylsilyl)thiophene-S,S-dioxide [31]. The latter material is of interest with regard to its photoluminescence

127

properties, and exhibits high efficiency blue fluorescence emission. The genetic algorithm technique has also been applied in the structure determination of a series of peptides, including Piv-Pro-Gly-NHMe [32] and Piv-Prog-Abu-NHMe [33]. Interest in the latter structure includes the fact that it contains an analogue of a b-turn, but constructed via an intramolecular C–H? ? ?O hydrogen bond. The Monte Carlo / simulated annealing strategy has been applied to solve several crystal structures, including structure determination of a number of pharmaceutical materials (some of significant conformational flexibility) [34], structural characterisation of four polymorphic forms of fananserine [35], and structure determination of tetracaine hydrochloride (a local anaesthetic) [36]. Among other examples, structure determination of a material containing one-dimensional spin chains obtained from 2,5bis(pyrazol-1-yl)-l,4-dihydroxybenzene and CuBr 2 in aqueous ammonia (comprising the purple coloured coordination polymer [1Cu] n ) has been reported [37]. Simulated Annealing has also been used to solve the structures of triphenyl phosphite [38], several polymorphs (with different colours) of 5-methyl-2-[(2-nitro-4methylphenyl)amino]-3-thiophenecarbonitrite [39], the low temperature (100 K) structure of S-camphor [40], and a number of other molecular crystal structures [41], and has also been used in combination with structure prediction (energy simulation) methods in the structure determination of metallo–organic complexes containing Zn, Cu and Ni [42]. The Monte Carlo method has been applied as part of a structural investigation of 5-bromonicotinic acid and solvates of 5-bromonicotinic acid [43], and in structure determination of 2,4,6-triisopropylbenzene sulfonamide and the 1:1 hydrogen-bonded adduct of hexamethylenetetramine and 1,2,3-trihydroxybenzene [44]. Finally, an interesting and challenging example [45] concerns the application of a simulated annealing approach to solve the structure of an organic:inorganic layered material containing 4-(4-dimethylamino-phenylazo)-1-methyl pyridinium as the guest component within a metal oxalate host structure. This material, which is of interest with regard to its non-linear optical properties, has 61 independent atoms in the asymmetric unit. The structure determined from the powder diffraction data provides a basis for rationalizing the properties of this material. Grid-search techniques have been applied to solve a number of structures, including several organometallic complexes [46–48] from laboratory and synchrotron X-ray powder diffraction data, and the molecular material 6phenyl - 5 - phenylsulfonyl - 1,2,3,4 - tetrahydropyrimidine - 2thione [49] from neutron powder diffraction data. Grid search methodology has also been employed, in combination with energy calculations and solid state NMR data, in order to determine the structure of anhydrous theophylline [50]. Other materials for which the crystal structures have

128

K.D.M. Harris / Current Opinion in Solid State and Materials Science 6 (2002) 125–130

been determined directly from powder diffraction data include decafluoroquaterphenyl [51], pentamethylcyclopentadienylsodium [52], a rigid ferrocenebased macrocycle [53], potassium and rubidium salicylate [54], caesium hydroxide monohydrate [55], pigment orange 2 [56], 8-hydroxy-5-nitroquinoline and 8-hydroxy5-nitroquinolinium chloride [57], and sodium 4-(2pyridinyl diazenyl)-resorcinolate monohydrate and ammonium 2,4-dinitro-1-naphthanenolate [58]. Structure determination from powder diffraction data has also led to an understanding of the thermal isomerisation pathway of 1 - (4 - nitrophenyl) - 2 - phenylimino - 2,5 - dihydro - 1H - pyrido[3,2,-b]indole-3-carbonitrite [59], and has been applied in studies of charge transfer complexes of metal dithiolenes [60]. Among several examples from the pharmaceutical field, powder diffraction has been used in characterization of the hydration properties of docetaxel [61].

4. Concluding remarks The wide-ranging examples of successful structure solution of molecular materials from powder diffraction data that have been reported in recent years, including those highlighted in this article, provide a clear demonstration of the increasing power, scope and applicability of the techniques available in this field. Through the application of these techniques, the option to determine molecular crystal structures directly from powder diffraction data is now a very real opportunity. Nevertheless, there remains considerable scope for further development and optimization of the techniques and strategies in this field, and it may be predicted with some confidence that the progress that has taken place in recent years will be maintained, with much vigour, in the years to come.

Acknowledgements I am grateful to Dr. Eugene Cheung for helpful discussions.

References [1] Harris KDM, Tremayne M, Kariuki BM. Contemporary advances in the use of powder X-ray diffraction for structure determination. Angew Chem Int Ed 2001;40:1626–51. [2] Chernyshev VV. Structure determination from powder diffraction. Russ Chem Bull Int Ed 2001;50:2273–92. [3] Toraya H. Crystal structure analysis using high-resolution synchrotron radiation powder diffraction data. J Ceram Soc Jpn 2001;109:903–10. [4] Porob DG, Row TNG. Ab initio structure determination via powder X-ray diffraction. Proc Ind Acad Sci Chem Sci 2001;113:435–44.

[5] Harris KDM. Structure determination of molecular crystals directly from powder diffraction data. Rigaku J 2001;18:23–32. [6] Neumann MA, Leusen FJJ, Engel GE, Wilke S, Conesa-Moratilla C. Recent advances in structure solution from powder diffraction data. Int J Mod Phys B 2002;16:407–14. [7] Hammond RB, Jones MJ, Roberts KJ, Smith EDL, Klapper H, Kutzke H, Docherty R, Cherryman J, Roberts RJ, Fagan PG. Determining the crystal structures of organic solids using X-ray powder diffraction together with molecular and solid state modeling techniques. Mol Cryst Liq Cryst 2001;56:389–405. [8] Kariuki BM, Harris KDM, Johnston RL. Solving crystal structures from powder diffraction data using genetic algorithms. Mol Cryst Liq Cryst 2001;356:469–81. [9] Harris KDM, Johnston RL, Kariuki BM, Tedesco E, Turner GW. Structure solution of molecular crystals from powder diffraction data using genetic algorithms: opportunities in academic and industrial research. Mater Sci Forum 2001;378–381:38–46. [10] Engel GE, Wilke S, Harris KDM, Kariuki BM, Ahn S, Leusen FJJ, Neumann MA. A simulated annealing approach for crystal structure solution from powder diffraction data. Mol Cryst Liq Cryst 2001;356:355–64. [11] Le Bail A. ESPOIR: a program for solving structures by Monte Carlo analysis of powder diffraction data. Mater Sci Forum 2001;378–381:65–70. [12] Cerny R. Powder pattern decomposition with the aid of preferred orientation – use of the whole Debye-Scherrer ring. Mater Sci Forum 2001;378–381:24–9. [13] Altomare A, Giacovazzo C, Moliterni AGG, Rizzi R. A random procedure for the decomposition of a powder pattern in EXPO. J Appl Crystallogr 2001;34:704–9. [14] Altomare A, Cuocci C, Giacovazzo C, Guagliardi A, Moliterni AGG, Rizzi R. Real-space technique applied to crystal structure determination from powder data. J Appl Crystallogr 2002;35:182–4. [15] Altomare A, Giacovazzo C, Ianigro M, Moliterni AGG, Rizzi R. Peak labelling in electron density maps from powder data: the use of crystal chemical information. J Appl Crystallogr 2002;35:21–7. [16] Brenner S, McCusker LB, Baerlocher C. The application of structure envelopes in structure determination from powder diffraction data. J Appl Crystallogr 2002;35:243–52. [17] Turner GW, Tedesco E, Harris KDM, Johnston RL, Kariuki BM. A method for understanding characteristics of multi-dimensional hypersurfaces, illustrated by energy and powder profile R-factor hypersurfaces for molecular crystals. Z Kristallogr 2001;216:187–9. [18] Habershon S, Harris KDM, Johnston RL, Turner GW, Johnston JM. Gaining insights into the evolutionary behaviour in genetic algorithm calculations, with applications in structure solution from powder diffraction data. Chem Phys Lett 2002;353:185–94. [19] Hsu HP, Hansmann UHE, Lin SC. Structure determination of organic molecules from diffraction data by simulated annealing. Phys Rev E 2001;64 (article no. 056707). [20] Seaton CC, Tremayne M. Differential evolution: crystal structure determination of a triclinic polymorph of adipamide from powder diffraction data. Chem Commun 2002:880–881. [21] Markvardsen AJ, David WIF, Johnson JC, Shankland K. A probabilistic approach to space-group determination from powder diffraction data. Acta Crystallogr Sect A 2001;57:47–54. [22] David WIF. Robust Rietveld refinement in the presence of impurity phases. J Appl Crystallogr 2001;34:691–8. ¨ D, Fontenas C, Elguero J. [23] Ochando LE, Amigo JM, Rius J, Louer The crystal structure of 3,5-diisopropyl-4-nitropyrazole from X-ray powder diffraction data. J Mol Struct 2001;562:11–7. [24] Brunelli M, Fitch AN, Jouanneaux A, Mora AJ. Crystal and molecular structures of norbornene. Z Kristallogr 2001;216:51–5. [25] Brunelli M, Fitch A, Mora AJ. Crystal structures of R-thiocamphor. Z Kristallogr 2002;217:83–7. [26] Tanahashi Y, Nakamura H, Yamazaki S, Kojima Y, Saito H, Ida T, Toraya H. Ab initio structure determination of monoclinic 2,2-

K.D.M. Harris / Current Opinion in Solid State and Materials Science 6 (2002) 125–130

[27]

[28]

[29]

[30]

[31]

[32]

[33]

[34]

[35]

[36]

[37]

[38]

[39]

[40]

[41]

[42]

dihydroxymethylbutanoic acid from synchrotron radiation powder diffraction data: combined use of direct methods and the Monte Carlo method. Acta Crystallogr B 2001;57:184–9. Yamazaki S, Toraya H. Determination of positions of zeolite calcium atoms and water molecules in hydrothermally formed aluminium-substituted tobermorite (1.1 nm) using synchrotron radiation powder diffraction data. J Am Ceram Soc 2001;84:2685–90. Nakamura H, Yamazaki S, Ohnishi T, Ida T, Toraya H. The Monte Carlo method for finding missing atoms in solving crystal structures from powder diffraction data without applying a rigid-body approximation. Powder Diffract 2001;16:65–70. Tedesco E, Dhillon SS, Harris KDM, Johnston RJ, Turner GW, Kariuki BM. Structure determination of 4,49-trimethylenedipyridine from powder diffraction data. Mater Sci Forum 2001;378–381:784– 8. Albesa-Jove´ D, Tedesco E, Harris KDM, Johnston RL, Cheung EY. Structural rationalization directly from powder diffraction data: intermolecular aggregation in 2-(methylsulfonyl)ethyl succinimidyl carbonate. Cryst Growth Des 2001;1:425–8. Tedesco E, Kariuki BM, Harris KDM, Johnston RL, Pudova O, Barbarella G, Marseglia EA, Gigli G, Cingolani R. Structural aspects of high-efficiency blue-emitting 2,5-bis(trimethylsilyl)thiophene-S,S-dioxide and related materials. J Solid State Chem 2001;161:121–8. Tedesco E, Harris KDM, Johnston RL, Turner GW, Raja KMP, Balaram P. Ab initio structure determination of a peptide beta-turn from powder X-ray diffraction data Chem Commun 2001;1460– 1461. Cheung EY, McCabe EE, Harris KDM, Johnston RL, Tedesco E, Raja KMP, Balaram P. C–H? ? ?O hydrogen bond mediated chain reversal in a peptide containing a g-amino acid residue, determined directly from powder X-ray diffraction data. Angew Chem Int Ed 2002;41:494–6. ¨ D, Leveiller F. Ab initio crystal Giovannini J, Perrin MA, Louer structure determination of three pharmaceutical compounds from X-ray powder diffraction data. Mater Sci Forum 2001;378– 381:582–7. Giovannini J, Ter Minassian L, Ceolin R, Toscani S, Perrin MA, ¨ D, Leveiller F. Tetramorphism of fananserine: p, T diagram Louer and stability hierarchy from crystal structure determinations and thermodynamic studies. J Phys IV 2001;11:123–6. Nowell H, Attfield JP, Cole JC, Cox PJ, Shankland K, Maginn SJ, Motherwell WDS. Structure solution and refinement of tetracaine hydrochloride from X-ray powder diffraction data. New J Chem 2002;26:469–72. Dinnebier R, Lerner HW, Ding L, Shankland K, David WIF, Stephens PW, Wagner M. One-dimensional spin chains from Cu-II ions and 2,5-bis(pyrazol-1-yl)-1,4-dihydroxybenzene. Z Anorg Allg Chem 2002;628:310–4. Hernandez O, Hedoux A, Lefebvre J, Guinet Y, Descamps M, Papoular R, Masson O. Ab initio structure determination of triphenyl phosphite by powder synchrotron X-ray diffraction. J Appl Crystallogr 2002;35:212–9. Pagola S, Stephens PW, He X, Byrn SR. Crystal structure solution of the dark red, light red and orange polymorphs of 5-methyl-2-[(2nitro-4-methylphenyl)amino]-3-thiophenecarbonitrile by high resolution X-ray powder diffraction and simulated annealing techniques. Mater Sci Forum 2001;378–381:789–94. Brunelli M, Fitch AN, Mora AJ. Low-temperature crystal structure of S-camphor solved from powder synchrotron X-ray diffraction data by simulated annealing. J Solid State Chem 2002;163:253–8. Zhukov SG, Chernyshev VV, Babaev EV, Sonneveld EJ, Schenk H. Application of simulated annealing approach for structure solution of molecular crystals from X-ray laboratory powder data. Z Kristallogr 2001;216:5–9. Bond AD, Jones W. Structure prediction as a tool for solution of the crystal structures of metallo-organic complexes using powder X-ray diffraction data. Acta Crystallogr B 2002;58:233–43.

129

˚ [43] Aakeroy CB, Beatty AM, Tremayne M, Rowe DM, Seaton CC. A combination of X-ray single-crystal diffraction and Monte Carlo structure solution from X-ray powder diffraction data in a structural investigation of 5-bromonicotinic acid and solvates thereof. Cryst Growth Des 2001;1:377–82. [44] Tremayne M, Maclean EJ, Glidewell C. Structure solution of hydrogen bonded molecular solids from powder diffraction data. Mol Cryst Liq Cryst 2002;356:215–25. [45] Evans JSO, Benard S, Yu P, Clement R. Ferroelectric alignment of NLO chromophores in layered inorganic lattices: structure of a stilbazolium metal-oxalate from powder diffraction data. Chem Mater 2001;13:3813–6. [46] Dova E, Stassen AF, Driessen RAJ, Sonneveld E, Goubitz K, Peschar R, Haasnoot JG, Reedijk J, Schenk H. Structure determination of the [Fe(teec) 6 ](BF 4 ) 2 metal complex from laboratory and synchrotron X-ray powder diffraction data with grid-search techniques. Acta Crystallogr B 2001;57:531–8. [47] Dova E, Goubitz K, van Langevelde A, Driessen R, Mahabiersing T, Blaauw R, Peschar R, Schenk H. Structure determination of two metal-organic complexes from high-resolution synchrotron powder diffraction data. J Synchrotron Rad 2001;8:1186–90. [48] Dova E, Goubitz K, Driessen R, Sonneveld E, Chernyshev V, Schenk H. Structure determination of two organometallic complexes from powder data using grid-search techniques. Mater Sci Forum 2001;378–381:798–801. [49] Rybakov VB, Chernyshev VV, Tafeenko VA, Shutalev AD, Kurbakov AI, Trounov VA. Synthesis and crystal structure determination of 6-phenyl-5-phenylsulfonyl-1,2,3,4-tetrahydropyrimidine-2-thione from neutron powder diffraction data. Z Kristallogr 2001;216:629– 32. [50] Smith EDL, Hammond RB, Jones MJ, Roberts KJ, Mitchell JBO, Price SL, Harris RK, Apperley DC, Cherryman JC, Docherty R. The determination of the crystal structure of anhydrous theophylline by X-ray powder diffraction with a systematic search algorithm, lattice energy calculations, and C-13 and N-15 solid state NMR: a question of polymorphism in a given unit cell. J Phys Chem B 2001;150:5818–26. ˇ [51] Smrcok L, Koppelhuber-Bitschnau B, Shankland K, David WIF, Tunega D, Resel R. Decafluoroquaterphenyl – crystal and molecular structure solved from X-ray powder data. Z Kristallogr 2001;216:63–6. [52] Tedesco C, Dinnebier RE, Olbrich F, van Smaalen S. Disordered crystal structure of pentamethylcyclopentadienylsodium as seen by high-resolution X-ray powder diffraction. Acta Crystallogr B 2001;57:673–9. [53] Dinnebier RE, Ding L, Ma KB, Neumann MA, Tanpipat N, Leusen FJJ, Stephens PW, Wagner M. Crystal structure of a rigid ferrocenebased macrocycle from high-resolution X-ray powder diffraction. Organometallics 2001;20:5642–7. [54] Dinnebier RE, Jelonek S, Sieler J, Stephens PW. The solid state structures of potassium and rubidium salicylate by high resolution X-ray powder diffraction. Z Anorg Allg Chem 2002;628:363–8. [55] Cerny R, Favre-Nicolin V, Bertheville B. A tetragonal polymorph of caesium hydroxide monohydrate, CsOH?H 2 O, from X-ray powder data. Acta Crystallogr C 2002;58:31–2. [56] Yatesenko AV, Paseshnichenko KA, Chernyshev VV, Schenk H. 1-[(2-Nitrophenyl)hydrazono]-1H-naphthalen-2-one (Pigment Orange 2) from powder data. Acta Crystallogr E 2001;57:01152–3. [57] Yatsenko AV, Paseshnichenko KA, Chernyshev VV, Schenk H. Powder diffraction study of the hydrogen bonds in nitroxoline and its hydrochloride. Acta Crystallogr C 2002;58:019–21. [58] Yatsenko AV, Paseshnichenko KA, Chernyshev VV, Schenk H. Sodium 4-(2-pyridinyldiazenyl)-resorcinolate monohydrate and ammonium 2,4-dinitro-1-naphthalenolate from powder diffraction data. Acta Crystallogr C 2001;57:397–9. [59] Chernyshev VV, Tafeenko VA, Ryabova SY, Sonneveld EJ, Schenk H. Thermal isomerization pathway of 1-(4-nitrophenyl)-2-

130

K.D.M. Harris / Current Opinion in Solid State and Materials Science 6 (2002) 125–130

phenylimino-2,5-dihydro-1H-pyrido[3,2-b]indole-3-carbonitrile discovered by laboratory powder data. Acta Crystallogr C 2001;57:982–4. [60] Kisch H, Eisen B, Dinnebier R, Shankland K, David WIF, Knoch F. Charge-transfer complexes of metal dithiolenes, part XXVII—chiral

metal-dithiolene / viologen ion pairs: synthesis and electrical conductivity. Chemistry 2001;7:738–48. [61] Zaske L, Perrin MA, Leveiller F. Docetaxel: solid state characterisation by X-ray powder diffraction and thermogravimetry. J Phys IV 2001;11:221–6.