Crystal Structure Solution from Powder Diffraction Data – State of the Art and Perspectives

An overview of contemporary methods of crystal structure solution from powder diffraction data is given. Methods are compared with respect to their advantages and disadvantages. A choice of an appropriate method is discussed in the light of understanding the structural problem to be solved. The need of the variety of methods for the variety of problems is illustrated by examples. Some directions of possible future development are discussed

Structure Determination by Joint Effort of X-ray Powder Diffraction and Quantum Calculations: Crystal Structure and Short Hydrogen Bonding in Pentadecafluorooctanoic Acid Hydrate

A precise X-ray crystal structure determination of systems that exist in a polycrystalline form often poses a challenge due to several factors that limit the resolution of the diffraction measurement. The location of atoms is usually determined at significantly lower precision than the unit cell parameters, rendering the complete characterization of the structure difficult. This is particularly pronounced when precise location of hydrogen atoms is required, for instance in ionizable biomolecules or in hydrogen bonds. In such cases periodic quantum (DFT) calculations may crucially assist structure determination, because they can reliably predict the location of atoms, provided that the unit cell parameters, the space group and tentative atomic positions are known. In this work we present DFT-assisted structure determination of pentadecafluorooctanoic acid hydrate, a benchmark system featuring short hydrogen bonds (RO...O ≈ 2.5 Å) between acid and water molecules. While Rietveld refinement based solely on powder diffraction data cannot reliably resolve the location of crystal water molecules and even less so the position of hydrogen atoms in the network of hydrogen bonds, periodic DFT optimization yields several minimum energy structures suitable for further refinement. Due to the low experimental resolution and similarity, comparison between model and experimental powder diffraction pattern can barely distinguish between certain structure candidates provided by DFT calculations, but it can rule out those featuring larger misfits. The proposed structure solution is delivered from a tandem application of structure determination from powder diffraction data and DFT optimization, the former providing the unit cell parameters and estimated atomic positions that are finely tuned by DFT. The present strategy can in principle be generalized to other examples of structure determination at relatively low resolution, such as is often the case with biological macromolecules. This work is licensed under a Creative Commons Attribution 4.0 International License

Nestehiometrijski bromo-kloro-piridin-MoIII kompleksi

By a selective exchange of ligand Br by Cl, a series of nonstoichiometric bromo-chloro-pyridine- molybdenum(III) octahedral compounds of the type (cat)[MoBraCl(4-a)py2] (cat = pyH, a = 3–1 (1, 4, 7)); cat = [(C2H5)3NH], a = 2.744 (2); cat = Rb, a = 2.278 (5); cat =[(C6H5)4)As], a = 1.258 (8) and [MoBraCl(3–a)py3] (a = 2–1 (3, 6)) have been prepared and characterized. Owing to great similarity of the powder diffraction patterns and IR spectra of compounds mer- [MoBraCl(3-a)py3] (a = 3–0) with the known monoclinic modification in the space group P21/c and compounds [MoBraCl(3-a)py3] (a = 2-1 (3, 6)), the same type of crystal lattice was confirmed. Isostructurality was observed also for the orthorhombic trans-(pyH)[MoBr4py2]](Pnma) and compounds 1 and 4, while compound 7 is isostructural to trans-(pyH)[MoCl4py2]. X-ray crystallographic analyses of 2, 5 and 8, obtained by recrystallization of (pyH)[MoBraCl(4-a)py2] (a = 3–1) with different cations, were performed. In these compounds, MoIII is octahedrally coordinated with four halogenido ions at distances 2.4953(6)–2.5920(10) Å and two pyridine molecules at distances 2.195(4)-2.220(4) Å. Trans oriented pyridine rings in compounds 5 and 8 are co-planar, while deviation from co-planarity was noticed for compound 2 (8.9(3)°). The stoichiometry of four coordinated Br and Cl atoms in these compounds is not ideal, since the structure analysis results for 2, 5 and 8 show a mixed occupancy of crystallographic sites; thus, refined population parameters for both atoms (Br and Cl) were calculated.Selektivnom zamjenom bromovoga liganda klorovim dobijena je i karakterizirana serija nestehiometrijskih bromo-kloro-piridin-MoIII kompleksa tipa (cat)[MoBraCl(4–a)py2] (cat = pyH, a = 3–1 (1, 4, 7); cat = [(C2H5)3NH], a = 2.744 (2); cat = Rb, a = 2.278 (5); cat = [(C6H5)4As], a = 1.258 (8)) i [MoBraCl(3–a)py3] (a = 2–1 (3, 6)). Uslijed velike sličnosti difraktograma praha i IR spektara spojeva mer-[MoBraCl(3–a)py3] (a = 3–0) poznate monoklinske modifikacije u prostornoj grupi P21/c i spojeva [MoBraCl(3–a)py3] (a = 2–1 (3, 6)), potvr|en je isti tip kristalne re{etke. Opa`ena je izostrukturnost rompskoga trans-(pyH)[MoBr4py2] (Pnma) i spojeva 1 i 4, dok je spoj 7 izostrukturiran s trans-(pyH)[MoCl4py2]. Načinjena je rentgenska strukturna analiza spojeva 2, 5 i 8 dobijenih prekristalizacijom (pyH)[MoBraCl(4–a)py2] (a = 3–1) s različitim kationima. U tim je spojevima MoIII oktaedarski koordiniran s četiri halogenidna iona na udaljenostima 2.4953(6)–2.5920(10) Å i dvije molekule piridina na udaljenostima 2.195(4)–2.220(4) Å. Trans orijentirani piridinski prstenovi u spojevima 5 i 8 su koplanarni dok je kod spoja 2 ustanovljena devijacija od koplanarnosti (8.9(3)°). Strukturnom analizom utočnjeni su faktori zauzetosti četiri koordinirana atoma (Br, Cl) u spojevima 2, 5 i 8. Na|eno je da su navedeni kristalografski položaji zauzeti atomima Cl i Br u nestehiometrijskome omjeru

Nestehiometrijski bromo-kloro-piridin-MoIII kompleksi

By a selective exchange of ligand Br by Cl, a series of nonstoichiometric bromo-chloro-pyridine- molybdenum(III) octahedral compounds of the type (cat)[MoBraCl(4-a)py2] (cat = pyH, a = 3–1 (1, 4, 7)); cat = [(C2H5)3NH], a = 2.744 (2); cat = Rb, a = 2.278 (5); cat =[(C6H5)4)As], a = 1.258 (8) and [MoBraCl(3–a)py3] (a = 2–1 (3, 6)) have been prepared and characterized. Owing to great similarity of the powder diffraction patterns and IR spectra of compounds mer- [MoBraCl(3-a)py3] (a = 3–0) with the known monoclinic modification in the space group P21/c and compounds [MoBraCl(3-a)py3] (a = 2-1 (3, 6)), the same type of crystal lattice was confirmed. Isostructurality was observed also for the orthorhombic trans-(pyH)[MoBr4py2]](Pnma) and compounds 1 and 4, while compound 7 is isostructural to trans-(pyH)[MoCl4py2]. X-ray crystallographic analyses of 2, 5 and 8, obtained by recrystallization of (pyH)[MoBraCl(4-a)py2] (a = 3–1) with different cations, were performed. In these compounds, MoIII is octahedrally coordinated with four halogenido ions at distances 2.4953(6)–2.5920(10) Å and two pyridine molecules at distances 2.195(4)-2.220(4) Å. Trans oriented pyridine rings in compounds 5 and 8 are co-planar, while deviation from co-planarity was noticed for compound 2 (8.9(3)°). The stoichiometry of four coordinated Br and Cl atoms in these compounds is not ideal, since the structure analysis results for 2, 5 and 8 show a mixed occupancy of crystallographic sites; thus, refined population parameters for both atoms (Br and Cl) were calculated.Selektivnom zamjenom bromovoga liganda klorovim dobijena je i karakterizirana serija nestehiometrijskih bromo-kloro-piridin-MoIII kompleksa tipa (cat)[MoBraCl(4–a)py2] (cat = pyH, a = 3–1 (1, 4, 7); cat = [(C2H5)3NH], a = 2.744 (2); cat = Rb, a = 2.278 (5); cat = [(C6H5)4As], a = 1.258 (8)) i [MoBraCl(3–a)py3] (a = 2–1 (3, 6)). Uslijed velike sličnosti difraktograma praha i IR spektara spojeva mer-[MoBraCl(3–a)py3] (a = 3–0) poznate monoklinske modifikacije u prostornoj grupi P21/c i spojeva [MoBraCl(3–a)py3] (a = 2–1 (3, 6)), potvr|en je isti tip kristalne re{etke. Opa`ena je izostrukturnost rompskoga trans-(pyH)[MoBr4py2] (Pnma) i spojeva 1 i 4, dok je spoj 7 izostrukturiran s trans-(pyH)[MoCl4py2]. Načinjena je rentgenska strukturna analiza spojeva 2, 5 i 8 dobijenih prekristalizacijom (pyH)[MoBraCl(4–a)py2] (a = 3–1) s različitim kationima. U tim je spojevima MoIII oktaedarski koordiniran s četiri halogenidna iona na udaljenostima 2.4953(6)–2.5920(10) Å i dvije molekule piridina na udaljenostima 2.195(4)–2.220(4) Å. Trans orijentirani piridinski prstenovi u spojevima 5 i 8 su koplanarni dok je kod spoja 2 ustanovljena devijacija od koplanarnosti (8.9(3)°). Strukturnom analizom utočnjeni su faktori zauzetosti četiri koordinirana atoma (Br, Cl) u spojevima 2, 5 i 8. Na|eno je da su navedeni kristalografski položaji zauzeti atomima Cl i Br u nestehiometrijskome omjeru

Solving Structural Problems of Ceramic Materials

Methods for the crystal structure determination from powder diffraction data are reviewed with special emphasis on the application to technical ceramics. Experimental techniques using other than laboratory X-ray, such as synchrotron radiation, neutron and electron beams, are also described. As an illustrative example, the crystal structure determinations of compounds LaNbTiO6, La0.462Nb0.614Ti0.386O3 and La0.37Nb0.889Ti0.111O3 in the ternary system of La2O3–Nb2O5–TiO2 are reported

Theoretical and Experimental Study of (Ba,Sr)TiO 3 Perovskite Solid Solutions and BaTiO 3 /SrTiO 3 Heterostructures

This study was supported by the ERA-NET HarvEnPiez project. The authors would like to thank their national funding agencies (Latvian State Education Development Agency, Slovenian Ministry of Higher Education, Science and Technology, Romanian National Authority for Scientific Research and Innovation, CCCDI-UEFISCDI, project number 49/2016 within PNCDI III – M-ERA NET Program).The results of experimental and theoretical ab initio study of structural and piezoelectric properties of (Ba,Sr)TiO3 perovskite solid solutions are discussed and compared. Experimentally, plate-like (Ba,Sr)TiO3 particles were synthesized by the topochemical conversion in the molten salt from Bi4Ti3O12 template plates. All dimensions (side length ≈ 1 µm, thickness ≈ 200–400 nm) were well above the critical size necessary for observation of piezo- and ferroelectricity. The first-principles computations of the structural and electromechanical properties of solid solutions were performed with CRYSTAL14 computer code within the linear combination of atomic orbitals (LCAO) approximation, using three advanced hybrid functionals of the density-functional-theory (DFT). Different chemical compositions are considered for the ferroelectric and paraelectric phases. Calculated structural properties of solid solutions in tetragonal and cubic phases are in a very good agreement with experimental data. Experimentally obtained and calculated band gaps are compared for cubic SrTiO3 and tetragonal BaTiO3. BaTiO3/SrTiO3 heterostructures were considered theoretically for different chemical compositions. The calculated piezoelectric properties of solid solutions and heterostructures in ferroelectric phase are compared. It is predicted that both solid solutions and heterostructures improve the piezoelectric properties of the bulk BaTiO3, but solid solutions are more preferable for equal Sr concentrations.ERA-NET HarvEnPiez project; Latvian State Education Development Agency, Slovenian Ministry of Higher Education, Science and Technology, Romanian National Authority for Scientific Research and Innovation, CCCDI-UEFISCDI, project number 49/2016 within PNCDI III – M-ERA NET Program; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Synthesis and Magnetic Properties of Hematite Particles in a ‘‘Nanomedusa’’ Morphology

We present the synthesis, characterization, and magnetic properties of hematite particles in a peculiar “nanomedusa” morphology. The particles were prepared from an iron-silica complex by a hydrothermal process in a solution consisting of ethyl acetate and ethanol. The particles’ morphology, structure, and chemical composition were investigated by transmission electron microscopy, powder X-ray diffraction, and scanning electron microscope equipped with an energy-dispersive X-ray spectrometer. The “hairy” particles consist of a spherical-like core of about 100 nm diameter and fibrous exterior composed of thin “legs” of 5 nm diameter grown along one preferential direction. The particles’ cores are crystalline and undergo a magnetic phase transition to a weakly ferromagnetic state at a temperature of 930K thatmatches reasonably the N´eel temperature of bulk hematite. However, unlike bulk hematite that undergoesMorin transition to an antiferromagnetic state around room temperature and small hematite nanoparticles that are superparamagnetic, the “nanomedusa” particles remain weakly ferromagnetic down to the lowest investigated temperature of 2K. Each particle thus represents a nanodimensional “hairy” ferromagnet in a very broad temperature interval, extending much above the room temperature. Such high-temperature ferromagnetic nanoparticles are not frequently found among the nanomaterials

Ammoniumbis(hydroxylammonium) pentafluoridooxidovanadate(IV)

Turquoise crystals of a new hydroxylammonium compound with the formula $NH_4(NH_3OH)_2[VOF_5]$ have been synthesized by the reaction of solid $NH_3OHF$ and the aqueous solution of vanadium in HF. The compound crystallizes monoclinic, $P2_1/n$, with cell parameters: a = 10.5658(2) Å, b = 6.6143(1) Å, c = 11.6618(2) Å, β = 96.282(1). Magnetic susceptibility was measured using a SQUID device over a temperature range 2–300 K at magnetic field $10^3 Oe$ giving the result $µ_{eff}$ = 1.65 BM. The thermal decomposition was studied by TG and DSC analysis. $NH_4(NH_3OH)_2[OF_5V]$ decomposes above 354 K in three steps, obtaining $NH_4VOF_3$ after the first step and $V_2O_5$ as the final residue.Z reakcijo med trdnim $NH_3OHF$ in raztopino vanadija v 40% HF smo sintetizirali turkizne kristale nove spojine hidroksilamina s formulo $NH_4(NH_3OH)_2[VOF_5]$. Spojina kristalizira monoklinsko, $P2_1/n$, s parametri osnovne celice: a = 10.5658(2) Å, b = 6.6143(1) Å, c = 11.6618(2) Å, β = 96.282(1). Iz meritev magnetne susceptibilnosti z magnetometrom SQUID v temperaturnem območju 2–300 K pri magnetnem polju $10^3 Oe$ smo izračunali efektivni magnetni moment $µ_{ef}$ = 1.65 BM. Termični razkroj spojine smo spremljali s TG in DSC analizo. $NH_4(NH_3OH)_2[OF_5V]$ nad temperaturo 354 K razpada v treh stopnjah preko vmesnega produkta $NH_4VOF_3$ do končnega preostanka $V_2O_5$

Formation and evolution of the hydrotalcite-like phase during ageing of dolomite-cement mortars under various conditions

This work considers the reactions of dolomite powder mixed with Portland cement during ageing under accelerating conditions (60 °C, water or alkaline medium). The phase composition and microstructure of cement-dolomite mortars were studied using X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy with X-ray microanalysis (SEM-EDS). The results showed that the alkalinity of the medium increased the dolomite reaction degree but did not affect the reaction products’ composition. The formation of the hydrotalcite-like phase with the gen-eral formula $Mg_4Al_2(CO_3)_{1−x}(OH)_{12+2x}·nH_2O$ proved to be the predominant route of dolomite consumption in the pres-ence of available aluminium in the hardened cement paste. Then, after three months of ageing, an interlayer anions re-placement became noticeable: carbonate anions in the structure of hydrotalcite are gradually replaced by hydroxide ones

Unique Electronic and Structural Properties of 1,4-Benzoquinones: Crystallochemistry of Alkali Chloranilate Hydrates

The unique electronic and structural characteristics of 1,4-benzoquinones with possibilities for numerous interactions such as coordination, hydrogen bonding accompanied by proton and/or electron transfer, π-interactions, and redox activity, are used by nature to perform important biological reactions. In spite of their wide use in supramolecular chemistry for construction of functional materials, the intercor-relation of their versatile interactions has not been completely evaluated. The impacts of hydrogen bonding and cations on interactions of quinoid skeleton are studied on the prepared series of alkali (Li+, Na+, K+, NH4+ and Rb+ chloranilate hydrates, and anhydrous caesium homologue. The π∙∙∙π stacking interactions of chloranilate dianions observed in the structures of sodium chloranilate dihydrate and caesium sodium chloranilate monohydrate [with centroid separation distances of 3.662(1) and 3.740(2) Å and shifts of 1.698 and 1.358 Å, respectively] are tuned by hydrogen bonding involving water molecules. The crystal structures of potassium and rubidium chloranilate monohydrates are isostructural whereas their ammonium homologue, due to the presence of cation with pronounced proton-donor activity, exhibits completely different hydrogen bonding network. In the six of seven structures studied chloranilate dianion reveals the crystallographic symmetry Ci