Aluminium tris(ethyl acetoacetate), Al(C6H9O3)(3) has been prepared and characterized by means of H-1 and C-13 nuclear magnetic resonance spectroscopy, scanning electron microscopy and X-ray powder diffraction (XRPD). It was determined that two stereoisomeric complexes can be distinguished in the solution: meridional and facial. The crystal structure of Al(C6H9O3)(3) has been determined from XRPD data. The compound crystallizes in the monoclinic space group P2(1)/n.

Ab initio crystal structure determination from powder diffraction data is not yet a straightforward process: it is strongly disrupted by the low quality of the estimated Bragg reflection intensities. In a two-stage method the integrated intensities calculated from a powder pattern are immediately submitted to direct methods to obtain phases. The larger the accuracy of the integrated intensities, the more efficient the phasing process. A systematic decomposition procedure was introduced in the EXPO2004 program to improve the efficiency of the phasing process. The disadvantage of this approach is that a large number of feasible trial structures are generated, among which the correct solution must be recognized. A new procedure is described aiming at introducing strategies to reduce the total number of trials to explore by defining an appropriate figure of merit able to regroup trial structures into different batches, each element of a batch sharing a high percentage of atoms with the other elements of the same batch. The new figure of merit, implemented in an updated version of EXPO2009, is able to discriminate non-solutions from promising trials, corresponding to incomplete or rough models which evolve, after refinement, into the correct solution.

A set of nine columbite samples (Fe,Mn)(Nb,Ta)(2)O-6, preserved in the Mineralogical Museum, Naples University Federico II (Italy) and originating from several world-wide pegmatitic occurrences, was studied by electron-probe microanalysis and single crystal X-ray diffraction. All the samples are columbite-(Fe), except for two samples corresponding to columbite-(Mn). For seven samples Ta/(Nb+Ta) is <0.05 and for two samples <0.2. The (Ti+Sn)(4+) content of all samples is <0.12 pfu. Structure refinements showed that five samples displayed strong (Fe,Mn)(2+) vs. (Nb,Ta)(5+) disorder at the two octahedral sites A and B, whereas four samples were highly ordered. Two samples could be interpreted as "pseudo-ixiolite". The degree of cation order at A and B was calculated from cell dimensions and scattering behaviour at A and B. Both methods are in good agreement. The octahedral coordination of (Nb, Ta)5+ in columbite is characterized by out-of-center distortion, thus the average distortion at the B site was probed by calculating the difference between the longest and shortest B-O distance. For a Nb-rich and (Ti,Sn)-poor data set, the min-max distortional parameter shows very good linear correlation with the order parameter calculated from site occupancy.

The EXPO package [1] is a computing program able to successfullyprovide the structure solution by starting from minimal information:the experimental powder diffraction pattern and the chemical formulaof the compound to investigate. EXPO can be used for solving organic,inorganic, metalorganic structures for a large variety of applications.Automation and efficiency are suitably combined in EXPO forperforming all the steps of the solution process: indexation, spacegroup determination, intensity extraction, structure solution, modeloptimization, Rietveld refinement.Automation. Default strategies, identified as the most effective,are selected for carrying out the solution process automatically andquickly. They may fail when the experimental data resolution is badand/or the structure complexity is remarkable. In these cases, EXPOcan promptly switch to appropriate strategies by profiting by a userfriendly graphical interface.Efficiency. Innovative theories and computing procedures aimingat making straightforward all the steps of the solution process areintegrated in EXPO and widely tested. EXPO is continuously updatedand optimized in terms of both computing efficiency and graphicalperformances.In EXPO the two stages based ab initio approach (in the first stagethe intensities are extracted; in the second, the reflections are phasedby Direct Methods) [2] is the automatic choice. The model providedby Direct Methods is usually partial and approximate because of wellknown unavoidable problems in powder diffraction (overlapping,background, preferred orientation). It can be optimized by default [3],[4] and/or non-default strategies [5], [6] which are able to reduce theerrors depending on the limited experimental resolution.A very recent study has regarded a new and more effective figureof merit [7], alternative to the classical one. It is able to pick up thephasing trial corresponding to the best solution among several feasibleones.Non ab initio method, requesting the knowledge of the expectedmolecular geometry and based on Simulated Annealing technique[8, 9], can optionally be attempted particularly in case of solution oforganic compounds.Examples of successful automatic runs by EXPO will be discussedin addition to available special strategies.

A new procedure (COVMAP) has been developed with the aim of recovering the full structure from very poor models, such as those provided by direct methods in unfavorable conditions. The procedure is based on the concept of covariance between points of an electron density map, mathematically set out by the authors in a recent paper: i.e. the density at one point depends on the density at another point of the map if their covariance is not vanishing. This concept suggested a procedure of electron density modification that uses pairs of model peaks to restrict the region where the density modification should be applied. Such modified densities lead to additional peaks, which in turn are submitted to two other important phasing tools present in EXPO2011, the resolution bias minimization and weighted least-squares procedures, which relocate, refine or reject these peaks. The procedure is cyclic and often leads to the correct structure even if the starting model is very poor.

Quite recently two papers have been published [Giacovazzo & Mazzone (2011). Acta Cryst. A67, 210218; Giacovazzo et al. (2011). Acta Cryst. A67, 368382] which calculate the variance in any point of an electron-density map at any stage of the phasing process. The main aim of the papers was to associate a standard deviation to each pixel of the map, in order to obtain a better estimate of the map reliability. This paper deals with the covariance estimate between points of an electron-density map in any space group, centrosymmetric or non-centrosymmetric, no matter the correlation between the model and target structures. The aim is as follows: to verify if the electron density in one point of the map is amplified or depressed as an effect of the electron density in one or more other points of the map. High values of the covariances are usually connected with undesired features of the map. The phases are the primitive random variables of our probabilistic model; the covariance changes with the quality of the model and therefore with the quality of the phases. The conclusive formulas show that the covariance is also influenced by the Patterson map. Uncertainty on measurements may influence the covariance, particularly in the final stages of the structure refinement; a general formula is obtained taking into account both phase and measurement uncertainty, valid at any stage of the crystal structure solution.

When dealing with the crystal structure solving of low-crystalline materials, it is of paramount importance to combine DFT geometry optimization with direct-space methods in order to find the correct structural model. Particularly, in the case of inorganic-organic hybrids prepared by solvothermal route, finite dimensional single crystal is very difficult to obtain. Hence, we present several successfully elucidated crystal structures from the powder XRD of the low-crystalline inorganic-organic hybrids: Cr(HL)Cl3, HL=Hbdmpza (1), [1] VO(C10H7COO)2 (2), VO(C14H9COO)2 (3). All of these structures have been solved from powder XRD data, either from laboratory or synchrotron source, by combining direct-space methods (simulated annealing), DFT geometry optimization, and constraint Rietveld refinement. The solid compound 1 was isolated in acetonitrile by starting CrCl3·9H2O and HL only in a concentrated solution, from which microcrystalline aggregates precipitated. Additionally, the presence of a carboxylate proton in HL stabilizes the structure by H-bonds, but also enables adsorption of moisture. Other two hybrids were synthesized in o-xylene by reacting vanadium (V) triisopropoxide with 1-naphthalenecarboxylic [2] or 9-anthracenecarboxylic acid. [2] They contain one-dimensional chain of corner-sharing tetrahedra in the case of VO(C10H7COO)2 (Figure 1(a), (c)), and corner-sharing octahedra for VO(C14H9COO)2 (Figure 1(b), (d)) oriented along orthorhombic/monoclinic c-axis, respectively. While VO(C14H9COO)2 exhibits bidentate bridging binding of organic moiety to the metal center, VO(C10H7COO)2 shows monodentate mode as evidenced from DFT and infrared spectroscopy. The obtained crystal structures were further verified by direct methods (ab initio approach). I. D. acknowledges financial support from the Unity through Knowledge Fund (www.ukf.hr) of the Croatian Ministry of Science, Education and Sports (Grant Agreement No. 7/13).

The title compound, C24H25NO3·2CH3OH, which crystallized as a methanol disolvate, has applications as a PET radiotracer in the early diagnosis of Alzheimer's disease. The dihedral angle between the biphenyl rings is 8.2 (2)° and the heterocyclic ring adopts a half-chair conformation with the N atom adopting a pyramidal geometry (bond-angle sum = 327.6°). The C atoms of both meth­oxy groups lie close to the plane of their attached ring [deviations = 0.107 (6) and 0.031 (6) Å]. In the crystal, the components are linked by O-H...O and O-H...N hydrogen bonds, generating [010] chains. C-H...O inter­actions are also observed.

alpha-Lithiated epoxides, long considered "fleeting" intermediates in the reactions of epoxides with strong bases, have nowadays proven to be key synthons for asymmetric synthesis. In this study, the solution and the solid state structure of an alpha-lithiated aryloxirane, namely a-lithiated ortho-trifluoromethyl styrene oxide (1-Li), were determined. Single crystal X-ray diffraction analysis of 1-Li performed at 100 K applying the X-TEMP-2 device revealed a self-assembled heterochiral dimeric structure with a rare central six-membered (O-Li-C)(2) planar core, which is unprecedented in Li/oxygen carbenoids. Multinuclear magnetic resonance (H-1, C-13, F-19, Li-7) studies suggested that 1-Li exists in THF solution as a mixture of two interconverting diastereomeric dimeric aggregates, each one featuring a single s-contact between lithium and a carbon atom. Line shape analysis provided activation parameters for both the dynamic interconversion of the two dimers and the enantiomerisation of 1-Li, which proved to be mostly entropy controlled. The structural assignment in solution was supported by density functional theory computations through the investigation of conformers of monomeric and dimeric complexes of 1-Li featuring different degrees of specific solvation. A mechanism based on the equilibration of six-membered homo-and heterochiral dimers was proposed to explain the configurational instability exhibited by 1-Li in THF.

ECS1@IYCr2014: Conveying a vision of modern crystallography Roberta Oberti, Serena Tarantino, Michele Zema, Marco Milanesio, Rita Berisio, Anna Moliterni, Carlo MealliThe first edition of the ECA European Crystallography School (ECS1), to be held in Pavia (Italy) during the course of IYCr2014, has found good balance between two apparently diverging goals: (i) to help students and young researchers to find their way in modern science, while keeping a special focus on the molecular and crystalline structure to interpret properties and functionality of materials; (ii) to raise the social and academic awareness of the great advances that crystallography has allowed and will allow to many branches of sciences.Students may choose between two formulae, i.e. a 6-day course with lectures and hands-on sessions held by renowned scientists, covering the state-of-the-art of crystallographic methods, theories and applications, at the same time indicating their future perspectives and cutting-edge aspects, or a 10-day Erasmus Intensive Programme, including a 3-day preparatory course and granting 3 ECTS credits.IYCr2014 is a unique opportunity to stimulate and ignite widespread interest in crystallography; therefore, some frontier seminars will be open to University faculty members, students, and to the general public. Efforts will be made to create a nice and friendly environment, with the goal to provide chances for future collaborations. Students will be invited to bring a poster showing their research results, projects or scientific interests. This will allow students to discuss their ideas with experienced crystallographers and favour aggregation.The programme received good support from scientific institutions and vendors, and a great response from the students: more than 110 pre-registrations from 33 countries were already received at the time this abstract was prepared, showing that there is a real need for both fundamental and advanced teaching in crystallography. We hope that this format will be continued and improved so as to provide a stable, periodic rendezvous for students and researchers under the common theme of crystallography.

Innovative methodologies, introduced in the software EXPO and working both in the reciprocal and in the direct space, can be successfully adopted for solving crystal structure by X-ray powder diffraction data. The principles underlying these methodologies are summarized. Three representative examples of crystal structure solution of the peptides Z-(Aib)(2)-OH, Z-(Aib)(3)-O-t-Bu and Z-(Aib)(4)-OH are discussed in relation to their different degree of structure complexity.

EXPO2011 is a new package for phasing crystal structures from powder diffraction diagrams. It is able to carry out all the steps necessary for crystal structure solution, from pattern indexation up to Rietveld method for structure refinement: for each step, the basic algorithm is described. Phasing is performed via ab initio (e.g., Direct Methods, integrated by real space refinement) and non ab initio techniques (e.g., simulated annealing algorithm, when molecular geometry is a priori known). Some emphasis is given to running procedures: the main commands and directives are described, to allow the user to run default and non-default phasing attempts.

EXPO2013, the heir of EXPO2009, has been enriched by a variety of new algorithms and graphical tools aiming at strengthening the individual steps of the powder structure solution pathway. Particular attention has been addressed to the procedures devoted to improving structural models provided by direct methods in ab initio approaches. In addition, a new procedure has been implemented, working in direct space, which may be chosen by the user as an alternative to the traditional simulated annealing algorithm. © 2013 International Union of Crystallography Printed in Singapore - all rights reserved.

Three new proton transfer compounds, [2-ammonio-5-methylcarboxybenzene perchlorate (1), (C8H10NO2+center dot ClO4-), 4-(ammoniomethyl)carboxybenzene nitrate (2), (C8H10NO2+center dot NO3-), and 4-(ammoniomethyl)carboxybenzene perchlorate (3), (C8H10NO2+center dot ClO4-)], have been synthesized, their IR modes of vibrations have been assigned and their crystal structures studied by means of single-crystal X-ray diffraction. Their asymmetric units consist of one cation and one anion for both compounds (1) and (2). However, the crystal structure of compound (3) is based on a pair of cations and a pair of anions in its asymmetric unit. The three-dimensional Hirshfeld surface analysis and the two-dimensional fingerprint maps revealed that the three structures are dominated by H center dot center dot center dot O/O center dot center dot center dot H and H center dot center dot center dot H contacts. The strongest hydrogen-bonding interactions are associated with O-H center dot center dot center dot O and N-H center dot center dot center dot O constituting the highest fraction of approximately 50%, followed by those of the H center dot center dot center dot H type contributing 20%. Other close contacts are also present, including weak C center dot center dot center dot H/H center dot center dot center dot C contacts (with about 10%).

Negli ultimi venticinque anni il metodo della diffrazione da polveri è stato applicato con successo crescente per risolvere strutture cristalline (composti organici, inorganici, metallorganici). Nonostante ciò, la soluzione strutturale da polveri è ancora oggi una sfida perché i problemi del metodo, dovuti principalmente all'interpretazione dei dati sperimentali, devono essere ancora risolti.

The phase identification of a polycrystalline mixture by X-ray powder diffraction data is often requested for studying materials interesting to different scientific and technological fields: chemistry, pharmaceutics, mineralogy, archeometry, forensic science, etc. The availability of user friendly computer programs, able to carry out qualitative phase analysis in efficient and possibly automatic way, is extremely useful to the scientific community involved in powder diffraction. QUALX2.0, the evolution of QUALX, is a freely distributed software for qualitative phase analysis. Based on the traditional search-match method, it is able to manage both a commercial database (PDF-2 maintained by ICDD), and a freely available database (POW_COD generated by the structure information contained in the Crystallography Open Database). QUALX2.0 is continuously improved in terms of computing and graphic tools. Correspondingly, the database POW_COD is suitably modified to make efficient the operations of search. The search-match approach can be facilitated by the use of restraints, when available, involving the chemical composition, the kind of compound(s) (e.g., organic, inorganic, etc.), the symmetry (space group, crystal system), the unit-cell parameters and/or volume, the crystal properties (measured and/or calculated crystal density, crystal color). An outline of the main features of QUALX2.0 and an example of application is described.

Rietveld refinement succeeds if the model is sufficiently close to the target structure. Severe distortions in the structural parameters or relatively high percentage of missed atoms do not allow the refinement to converge. Ab initio techniques like Direct or Patterson methods may rely only on the reflection intensities provided by full pattern decomposition algorithms. Owing to the relevant errors in the intensity estimates, the structural models provided by such phasing techniques are poor and require supplementary improvements before being submitted to Rietveld refinement. The situation is more favorable for non-ab initio techniques, when they can exploit the prior information on the full molecular geometry: their models can be easily submitted to Rietveld refinement, but often the accuracy of the refined model relies on the geometrical information rather than on the experiment. In this paper ab natio and non-ab initio phasing tools of EXPO2011, the updated and more powerful version of EXPO2009 [1], are described together with ancillary techniques for improving and completing the structural models.

Herein we report a new straightforward synthesis of cis and trans 2,5-disubstituted N,N-dialkylpiperazines, even in enantioenriched form, by reacting non-activated N-alkyl arylaziridines in the presence of a catalytic amount of a Lewis acid. A stereochemical and NMR investigation revealed useful mechanistic insights for this process.

The study describes a targeted synthesis of a new dielectric material for an emerging ULTCC-I technology (ultralow temperature co-fired ceramic technology), which resulted in discovery of a PbTeV2O8 phase. A structural solution from powder data showed that the phase belongs to no known crystallographic family and is formed from Vs+ ions in an unusual square-pyramidal coordination. It is characterized by very low processing temperatures that enable integration with Al electrodes and, potentially, even with polymer and paper substrates. Dielectric properties in combination with processing parameters qualify the PbTeV2O8 phase for integration, as midpermittivity capacitors, in ULTCC-I modules.

QUALX2.0 is the new version of QUALX, a computer program for qualitative phase analysis by powder diffraction data. The previous version of QUALX was able to carry out phase identification by querying the PDF-2 commercial database. The main novelty of QUALX2.0 is the possibility of querying also a freely available database, POW_COD. POW_COD has been built up by starting from the structure information contained in the Crystallography Open Database (COD). The latter is a growing collection of diffraction data, freely downloadable from the web, corresponding to inorganic, metal-organic, organic and mineral structures. QUALX2.0 retains the main capabilities of the previous version: (a) automatically estimating and subtracting the background; (b) locating the experimental diffraction peaks; (c) searching the database for single-phase pattern(s) best matching to the experimental powder diffraction data; (d) taking into account suitable restraints in the search; (e) performing a semi-quantitative analysis; (f) enabling the change of default choices and strategies via a user-friendly graphic interface. The advances of QUALX2.0 with respect to QUALX include (i) a wider variety of types of importable ASCII file containing the experimental diffraction pattern and (ii) new search-match options. The program, written in Fortran and C++, runs on PCs under the Windows operating system. The POW_COD database is exported in SQLite3 format.

The new method RAMM (random-model-based method) has been developed and implemented in the EXPO computing program for improving the ab initio crystal structure solution process. When the available information consists of only the experimental powder diffraction pattern and the chemical formula of the compound under study, the classical structure solution approach follows two main steps: (1) phasing by direct methods (or by Patterson methods) in order to obtain a structure model (this last is usually incomplete and/or approximate); (2) improving the model by structure optimization techniques. This article proposes the alternative procedure RAMM, which skips step (1) and supplies a fully random model to step (2). This model is then submitted to effective structure optimization tools present in EXPO - wLSQ (weighted least squares), RBM (resolution bias minimization) and COVMAP (a procedure of electron density modification based on the concept of covariance between points of the map) - which are able to lead to the correct structure. RAMM is based on a cyclic process, generating several random models which are then optimized. The process stops automatically when it recognizes the correct structure.

The Shift_and_Fix procedure is a new method which has been developed for improving the quality of a structure model obtained by the ab-initio solution process from powder diffraction data. The main features of the new approach, which is fully automatic, are: a) the structure model usually attained at the end of the phasing process by Direct Methods is shifted partly and randomly; b) a combination of Fourier map calculation and least squares cycles has been suitably designed for relocating the shifted atoms onto positions which can finally be moved onto the true ones by the standard model optimization approaches; c) the Fourier map is calculated using coefficients which depend on the chemical content of the compound under study. When the figure of merit for selecting the best set of phases derived by Direct Methods does not work well, the ALLTRIALS strategy can be applied: it aims at investigating, automatically and sequentially, all the stored Direct Methods phasing sets and picking up the correct solution. The Shift_and_Fix method has been applied for improving the structure model calculated by each one of the phasing sets processed by ALLTRIALS. It has been implemented in the computing program EXPO and proved to be effective in providing a better ALLTRIALS outcome and increasing the probability of succeeding in the ab-initio powder solution.

A highly stereo- and regioselective functionalisation of chiral non-racemic aziridines is reported. By starting from a parent enantioenriched aziridine and finely tuning the reaction conditions, it is possible to address the regio- and stereoselectivity of the lithiation/electrophile trapping sequence, thereby allowing the preparation of highly enantioenriched functionalised aziridines. From chiral N-alkyl trans-2,3-diphenylaziridines (S,S)-1a,b, two differently configured chiral aziridinyl-lithiums could be generated (trans-1a,b-Li in toluene and cis-1a,b-Li in THF), thus disclosing a solvent-dependent reactivity that is useful for the synthesis of chiral tri-substituted aziridines with different stereochemistry. In contrast, chiral aziridine (S,S)-1c showed a temperature-dependent reactivity to give chiral ortho-lithiated aziridine 1c-ortho-Li at -78 degrees C and alpha-lithiated aziridine 1c-alpha-Li at 0 degrees C. Both lithiated intermediates react with electrophiles to give enantioenriched ortho- and alpha-functionalised aziridines. The reaction of all the lithiated aziridines with carbonyl compounds furnished useful chiral hydroxyalkylated derivatives, the stereochemistry of which was ascertained by X-ray and NMR spectroscopic analysis. The usefulness of chiral non-racemic functionalised aziridines has been demonstrated by reductive ring-opening reactions furnishing chiral amines that bear quaternary stereogenic centres and chiral 1,2-, 1,3- and 1,5-aminoalcohols. It is remarkable that the solvent-dependent reactivity observed with (S,S)-1a,b permits the preparation of both the enantiomers of amines (11 and ent-11) and 1,2-aminoalcohols (13 and ent-13) starting from the same parent aziridine. Interestingly, for the first time, a configurationally stable chiral alpha-lithiated aziridine (1c-alpha-Li) has been generated at 0 degrees C. In addition, ortho-hydroxyalkylated aziridines have been easily converted into chiral aminoalkyl phthalans, which are useful building blocks in medicinal chemistry.

Aziridines are widely used as versatile building blocks for the synthesis of a variety of biologically and pharmaceutically importantmolecules [1]. Among the available methodologies for the preparation of functionalised aziridines, the lithiation/trapping sequence of simpleparent aziridines is growing in importance [2]. Present work reports the results concerning the structural study of aziridine-2-methanolderivatives by dynamic nuclear magnetic resonance (DMNR) [3] and single crystal X-ray diffraction. A careful examination of the aziridine2 (see figure 1) by NMR data, shows that at room temperature the meta protons and the protons of the two ortho methyl groups of the mesitylring gives featureless lumps, likely as consequence of a restricted rotation around the Csp3 -Csp2 bond between the carbinolic carbon andthe ipso carbon of the mesityl ring. Also in the solid state, an almost identical arrangement of the mesityl ring, with respect to the other twophenyl rings, has been observed. In this case, the aziridine nitrogen substituent was found in a syn relationship with respect to the carbinolicgroup so preventing the possibility of forming a hydrogen bond with the hydroxyl group. This evidence underlines a slow rotation of themesityl group instead of a nitrogen inversion as usually is expected. By X-ray analysis of 3 and diast-3 (figure 1), it is estimated that thenitrogen substituents set on the opposite side with respect the carbinolic carbon. Via study of crystal structures, the presence of hydrogenbonds between the hydroxyl group and the aziridine nitrogen lone pair was ascertained for aziridine 3 but not for diast-3 (figure 1). Such a hydrogen bond, which is persistent also in solution, could prevent the formation of conformational diastereoisomers by rotation around the bond between the carbinolic carbon and the aziridine quaternary carbon. This hypothesis has been demonstrated by NMR experiments. This investigation allowed us to calcolate some Csp2-Csp3 and Csp3-Csp3 rotational barriers and highlight a sort of "geared" rotation between aryl and alkyl substituents; this is possible if the structure is not in a locked conformation by an hydrogen bond as demonstrated by NMR and X-ray diffraction.

A reciprocal-space resolution bias correction algorithm has been recently suggested, providing suitable corrections for the classical atomic scattering factors. The Fourier maps calculated by using as coefficients the structure factors obtained by the modified scattering factors proved to be less resolution biased. In this paper the correction has been generalized in order to apply it to the experimental structure factor moduli; in this way more useful electron density maps may be calculated. In a less recent paper a direct-space resolution bias correction algorithm was devised and tested on a large set of powder patterns; the algorithm implies the modification of the electron density maps to reduce the truncation errors in the Fourier syntheses. In the present paper direct and reciprocal resolution bias correction algorithms are combined into the dual-space resolution bias correction algorithm. The usefulness of the new algorithm is checked on a set of powder patterns.

The limited resolution of experimental diffraction data distorts the Fourier synthesis so that the electron density map obtained by the structure factors is an imperfect representation of the true density: the worse the experimental resolution, the less accurate the Fourier representation. We have recently developed new methods aiming at reducing the resolution effects by correcting it both in the Reciprocal Space (RS) and in the Direct Space (DS): e.g., by modifying the atomic scattering factors in RS and the electron density map in DS. The Dual-Space (DUS) method combines the RS and DS procedures. In addition, new computing strategies have been developed for improving the Fourier map calculation. The DUS algorithm has been introduced in the EXP02010 package in order to obtain more reliable structure models. It has been successfully applied to several test structures. The main features of the new procedure and the results of our applications will be described.

The big bang-big crunch method is a global optimization approach developed upon the analogy of one of the cosmological theories of the evolution of the universe. It has been suitably combined with a simulated annealing algorithm and used for solving crystal structure from powder diffraction data in direct space. When compared with the traditional simulated annealing method, it provides a significant advance: good solutions are attained in a shorter time. The new method has been implemented in the EXPO package. Its successful application is demonstrated with examples of already known structures.

Anatase (TiO?) and multiwalled carbon nanotubes bearing polyethylenimine (PEI) anchored on their surface were hybridized in different proportions according to a sol-gel method. The resulting nanocomposites (TiO?@PEI-MWCNTs), characterized by BET, XRD, XPS, SEM, and UV techniques, were found efficient catalysts for CO? photoreduction into formic and acetic acids in water suspension and under visible light irradiation. PEI-grafted nanotubes co-catalysts are believed to act as CO? activators by forming a carbamate intermediate allowing to accomplish the first example in the literature of polyamines/nanotubes/TiO? mediated CO? photoreduction to carboxylic acids