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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The article describes an atom-matching-based figure of merit (AMB FOM) which was developed and implemented in the EXPO2009 systematic decomposition program in order to enhance the efficiency of the crystal phasing process. The disadvantages and limited ability of the standard FOM are explored. According to the authors, one of the advantages of using the AMB FOM is its ability to regroup trial solutions in batches, which collect trials with models sharing a high percentage of atoms.

Powder pattern indexing can still be a challenge, despite the great recent advances in theoretical approaches, computer speed and experimental devices. More plausible unit cells, belonging to different crystal systems, are frequently found by the indexing programs, and recognition of the correct one may not be trivial. The task is, however, of extreme importance: in case of failure a lot of effort and computing time may be wasted. The classical figures of merit for estimating the unit-cell reliability {i.e. M20 [de Wolff (1968). J. Appl. Crys 108-113] and FN [Smith & Snyder (1979). J. Appl. Cryst. 12, 60-65]} sometimes fail. For this reason, a new figure of merit has been introduced in N-TREOR09, the updated version of the indexing package N-TREOR [Altomare, Giacovazzo, Guagliardi, Moliterni, Rizzi & Werner (2000). J. Appl. Cryst. 33, ]180-]186 combining the information supplied by M20 with additional parameters such as the number of unindexed lines, the degree of overlap in the pattern (the so- called number of statistically independent observations), the symmetry deriving from the automatic evaluation of the extinction group, and the agreement between the calculated and observed profiles. The use of the new parameters requires a dramatic modification of the procedures used worldwide: in the approach presented here, extinction symbol and unit-cell determination are simultaneously estimated. N-TREOR09 benefits also from an improved indexing procedure in the triclinic system and has been integrated into EXP02009, the updated version of EXP02004 [Altomare, Caliandro, Camalli, Cuocci, Giacovazzo, Moliterni & Rizzi (2004). J. Appl. Cryst. 37, 1025-]028] The application of the new procedure to a large set of test structures is described. [ABSTRACT FROM AUTHOR]

A new joint probability distribution function method is described to find the anomalous scatterer substructure from powder data. The method requires two wavelengths; the conclusive formulas provide estimates of the substructure structure factor moduli, from which the anomalous scatterer positions can be found by Patterson or direct methods. The theory has been preliminarily applied to two compounds, the first having Pt and the second having Fe as anomalous scatterer. Both substructures were correctly identified. [ABSTRACT FROM AUTHOR]

The electron density map produced after the application of direct methods to powder diffraction data of organic compounds is usually very approximated: some atoms are missed, other atoms are in false positions, some atoms are imperfectly located and the connectivity is quite low. A new procedure able to recover the complete structure model is described. In this procedure, a better interpretation of the map is combined with geometrical techniques for generating new atomic positions. The application of the new procedure may lead to the recovery of the complete crystal structure. [ABSTRACT FROM AUTHOR]

The Rietveld method is the most widely used approach for refining crystal structures from powder diffraction patterns. It requires sufficiently accurate structure models and user skill. A method is described which is often able to complete and refine a structure model by using an automatic least-squares procedure applicable to reflection integrated intensities. A weighting scheme has been devised that is capable of taking into account the lower accuracy of the estimates of the overlapping reflections. [ABSTRACT FROM AUTHOR]

EXP02004 is the updated version of the EXPO program [Altomare et al. (1999). Z AppL Cryst. 32, 339–340]. The traditional steps of the ab initio powder solution process are performed automatically: indexing, space-group determination, decomposition of the pattern for extracting the observed structure-factor moduli, structure solution by direct methods, model refinement by Rietveld technique. Special strategies may be applied to improve both the estimates of the extracted structure-factor moduli and the quality of the structure model. In addition, the use of special procedures exploiting available supplementary information on molecular geometry can be successfully adopted. The graphical interface has also been improved. [ABSTRACT FROM AUTHOR]

Focuses on the peak labelling of electron density. Refinement of crystal structure; Impact of incorrect labelling on crystal structure; Representation of the electron density.

Examines the code associated to the program N-TREOR in order to define an efficient peak search procedure. Techniques used for the indexing of a powder diffraction pattern; Modification of the crystallographic decisions; Availability of N-TREOR as a stand-alone program.

Layered (2D) perovskites are an emerging attractive 2D system with enhanced stability to ambient conditions as opposed to their highly unstable three dimensional bulk counterpart. Their uniquely tuneable optical and electrical properties are underpinning a surge of interest in 2D‐photovoltaics. So far, the development of nano‐scale integrated opto‐electronic 2D perovskite devices remains nearly unexplored since they have generally been found to be incompatible with standard top‐down semiconductor nano‐fabrication technologies. Here, following the synthesis of solvent‐stable 2D‐fluorinated phenethylammonium lead iodide perovskite (F‐PEA)2PbI4 (F‐PEAI), planar photodetectors entirely fabricated in atmosphere is demonstrated, exhibiting figures of merit rivalling those of commercial silicon photodiodes. A record large room temperature detectivity (>5 × 1017 Jones), a fast time photoresponse (rise time 1.5 ns), an extraordinarily large linear dynamic range (228 dB), as well as a photo‐responsivity of ≈ 1100 AW−1 are demonstrated for devices on a range of substrates including flexible wearable media without the need for any planarization or any atomically thin dielectric, in stark contrast to other 2D semiconductors. Finally, the suitability of nano‐scale 2D F‐PEAI photodetector arrays with sub‐wavelength pixel size of just 100 nm of use for high definition imaging is demonstrated. [ABSTRACT FROM AUTHOR]

New approaches have been introduced in the EXPO2007 program aiming at making easier and straightforward the ab initio crystal structure solution from powder diffraction data. Improvements in space group determination, powder pattern decomposition, least squares Fourier recycling, interpretation of the electron density map have been developed. To manage organic crystal structures a new strategy in direct-space, combining Direct Methods and Simulated Annealing approaches, has been implemented. [ABSTRACT FROM AUTHOR]

Reactions of Zeise’s salt (K[Pt(η2-C2H4)Cl3]) with oxidized phenanthroline ligands (1,10-phenanthroline-5,6-dione, phedon, and 2,9-dimethyl-1,10-phenanthroline-5,6-dione, Me2phedon) are reported. Comparison with analogous reactions involving unoxidized phen (1,10-phenanthroline) and Me2phen (2,9-dimethyl-1,10-phenanthroline) ligands indicates that these latter ligands are less capable to stabilize the five-coordinate species [PtCl2(η2-C2H4)(phenanthroline)] in which the phenanthroline and the olefin share the trigonal plane and two chlorines are in the axial positions. The X-ray structure of the four-coordinate species [PtCl2(Me2phedon)] indicates that the major difference between oxidized and unoxidized phenanthrolines is the loss of aromaticity of the central ring of phenanthroline. As a consequence, the oxidized phenanthroline becomes more flexible and can undergo a bow-like distortion so to reduce steric interaction between ortho substituents of phenanthroline and cis chlorine ligands. The increase in stability of the four-coordinate species with Me2phedon is concomitant with an increase in stability of the five-coordinate precursor complex with ethylene. In the latter case the stabilization is not of sterical origin but stems from reduced electron-donor properties of oxidized phenanthrolines. The balance of the two effects is such that the equilibrium between five- and four-coordinate species is more shifted in favour of the former species in the case of Me2phedon than in the case of Me2phen. [Copyright &y& Elsevier]

A novel double-open-cubane (NNCO) 6 Co 4 Cl 2 cluster with a Co 4 O 6 core was made available under aqua-ultrasonic open atmosphere conditions for the first time. The ultrasonic clusterization of the (3,5-dimethyl-1 H -pyrazol-1-yl)methanol (NNCOH) ligand with CoCl 2 ·6H 2 O salts in ethanol yielded a high-purity and high-yield cluster product. Energy-dispersive X-ray (EDX), Fourier transform infrared (FT-IR), and ultraviolet (UV)-visible techniques were used to elucidate the clusterization process. The double-open-Co 4 O 6 cubane structure of the (NNCO) 6 Co 4 Cl 2 cluster was solved by synchrotron single-crystal X-ray diffraction (SXRD) and supported by density functional theory (DFT) optimization and thermogravimetric/differential TG (TG/DTG) measurements; moreover, the DFT structural parameters correlated with the ones determined by SXRD. Molecular electrostatic potential (MEP), Mulliken atomic charge/natural population analysis (MAC/NPA), highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO), density of states (DOS), and GRD quantum analyses were computed at the DFT/B3LYP/6-311G(d,p) theory level. The thermal behavior of the cluster was characterized to support the formation of the Co 4 O 6 core as a stable final product. The catalytic property of the (NNCO) 6 Co 4 Cl 2 cluster was predestined for the oxidation process of 3,5-DTBC diol (3,5-di- tert -butylbenzene-1,2-diol) to 3,5-DTBQ dione (3,5-di- tert -butylcyclohexa-3,5-diene-1,2-dione)., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Here we present a colloidal approach to synthesize bismuth chalcohalide nanocrystals (BiEX NCs, in which E=S, Se and X=Cl, Br, I). Our method yields orthorhombic elongated BiEX NCs, with BiSCl crystallizing in a previously unknown polymorph. The BiEX NCs display a composition-dependent band gap spanning the visible spectral range and absorption coefficients exceeding 10 5  cm -1 . The BiEX NCs show chemical stability at standard laboratory conditions and form colloidal inks in different solvents. These features enable the solution processing of the NCs into robust solid films yielding stable photoelectrochemical current densities under solar-simulated irradiation. Overall, our versatile synthetic protocol may prove valuable in accessing colloidal metal chalcohalide nanomaterials at large and contributes to establish metal chalcohalides as a promising complement to metal chalcogenides and halides for applied nanotechnology., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

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 meth-oxy 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 inter-actions are also observed.

Quite recently two papers have been published [Giacovazzo & Mazzone (2011). Acta Cryst. A67, 210-218; Giacovazzo et al. (2011). Acta Cryst. A67, 368-382] 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.

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)-1 a,b, two differently configured chiral aziridinyllithiums could be generated (trans-1 a,b-Li in toluene and cis-1 a,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)-1 c showed a temperature-dependent reactivity to give chiral ortho-lithiated aziridine 1 c-ortho-Li at -78 °C and α-lithiated aziridine 1 c-α-Li at 0 °C. Both lithiated intermediates react with electrophiles to give enantioenriched ortho- and α-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)-1 a,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 α-lithiated aziridine (1 c-α-Li) has been generated at 0 °C. In addition, ortho-hydroxyalkylated aziridines have been easily converted into chiral aminoalkyl phthalans, which are useful building blocks in medicinal chemistry., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The joint probability distribution function method is applied to multiple-wavelength anomalous dispersion (MAD) powder data. The distributions are calculated by assuming prior knowledge of the scattering intensities at two wavelengths and of the anomalous-scatterer substructure. The method leads to formulas estimating the full structure phases and their reliability. The procedure has been applied to two structures, one unknown and one known; the second was used as a control for the phasing procedure. In spite of the unavoidable peak overlapping in the diffraction pattern, the formulas proved to be very effective. Combined with a new algorithm for phase extension, they enabled the solution of both crystal structures.

Fourier syntheses are always affected by series-termination errors, which generate sets of positive and negative ripples around each main peak in the map. The interaction among the ripples distorts the profile of the map and moves peaks away from their correct positions. In a previous paper [Altomare et al. (2008). Acta Cryst. A64, 326-336] an algorithm was described which reduces the resolution bias by removing the effects of the ripples in direct space. In this paper the correction is performed in reciprocal space: the effect of the ripples on the atomic scattering factors is calculated and subtracted from the usual atomic scattering factors. The modified scattering factors are used to calculate new structure factors, from which more accurate electron-density maps may be obtained. The experimental tests show that the procedure minimizes the effects of the resolution bias and provides atomic positions that are more accurate than those provided by traditional approaches.

Electron-density maps are calculated by Fourier syntheses with coefficients based on structure factors. Diffraction experiments provide intensities up to a limited resolution; as a consequence, the Fourier syntheses always show series-termination errors. The worse the resolution, the less accurate is the Fourier representation of the electron density. In general, each atomic peak is shifted from the correct position, shows a deformed (with respect to the true distribution of the electrons in the atomic domain) profile, and is surrounded by a series of negative and positive ripples of gradually decreasing amplitude. An algorithm is described which is able to reduce the resolution bias by relocating the peaks in more correct positions and by modifying the peak profile to better fit the real atomic electron densities. Some experimental tests are performed showing the usefulness of the procedure.

Dibarium micro-oxido-bis[pentachloridoruthenate(IV)] decahydrate, Ba(2)Ru(2)Cl(10)O.10H(2)O, has been prepared from ruthenium(III) chloride and barium chloride in hydrochloric acid. It crystallizes in the monoclinic system (space group C2/c). The structure consists of alternating layers of [Ru(2)Cl(10)O](4-) and [Ba(H(2)O)(7)](2+) complex ions along the a direction. The O atom bonded to ruthenium occupies the 4e site, with 1 symmetry, while the other atoms occupy general 8f sites. The overall structure is held together by O-H...O hydrogen bonds and O-H...Cl dipole-dipole interactions.

Mg2Ru2Cl10O.16H2O {dimagnesium mu-oxo-bis[pentachlororuthenate(IV)] hexadecahydrate} crystallizes in the monoclinic system (space group P2(1)/c). The structure consists of layers of [Ru2Cl10O]4- anions, [Mg(H2O)6]2+ cations and water molecules stacked along the a axis. Only the O atom bonded to Ru occupies the 2a site with -1 symmetry. All the other atoms occupy general 4e sites. The crystal structure is stabilized by O-H...O and O-H...Cl interactions.