Characterization and ab Initio XRPD Structure Determination of a Novel Silicate with <i>V</i><i>ierer</i> Single Chains: The Crystal Structure of NaYSi₂O₆

The crystal structure of a sodium yttrium silicate with composition NaYSi2O6 has been determined from laboratory X-ray powder diffraction data by simulated annealing, and has been subsequently refined with the Rietveld technique. The compound is monoclinic with space group P21/c and unit cell parameters of a = 5.40787(2) Å, b = 13.69784(5) Å, c = 7.58431(3) Å, and β = 109.9140(3)° at 23.5 °C (Z = 4). The structure was found to be a single-chain silicate with a chain periodicity of four. The two symmetry dependent [Si4O12] chains in the unit cell are parallel to c. A prominent feature is the strong folding of the crankshaft-like chains within the b,c-plane resulting in intrachain Si−Si−Si angles close to 90°. The coordination of the Y3+ ions by O2- is 7-fold in the form of slightly irregular pentagonal bipyramids, with oxygen atoms from four different chains contributing to the coordination polyhedron. Na+ ions are irregularly coordinated by 10 oxygens from two neighboring chains. No disorder of Na+ and Y3+ between the two nontetrahedral cation sites could be observed. Furthermore, micro-Raman spectra have been obtained from the polycrystalline material

Structural, Spectroscopic, and Computational Studies on Tl₄Si₅O₁₂: A Microporous Thallium Silicate

Single crystals of the previously unknown thallium silicate Tl₄Si₅O₁₂ have been prepared from hydrothermal crystallization of a glassy starting material at 500 °C and 1kbar. Structure analysis resulted in the following basic crystallographic data: monoclinic symmetry, space group <i>C</i>2/<i>c</i>, <i>a</i> = 9.2059(5) Å, <i>b</i> = 11.5796(6) Å, <i>c</i> = 13.0963(7) Å, β = 94.534(5)°. From a structural point of view the compound can be classified as an interrupted framework silicate with Q³- and Q⁴-units in the ratio 2:1. Within the framework 4-, 6-, and 12-membered rings can be distinguished. The framework density of 14.4 T-atoms/1000 ų is comparable with the values observed in zeolitic materials like Linde type A, for example. The thallium cations show a pronounced one-sided coordination each occupying the apex of a distorted trigonal TlO₃ pyramid. Obviously, this reflects the presence of a stereochemically active 6s² lone pair electron. The porous structure contains channels running along [110] and [−1 1 0], respectively, where the Tl⁺ cations are located for charge compensation. Structural investigations have been completed by Raman spectroscopy. The interpretation of the spectroscopic data and the allocation of the bands to certain vibrational species have been aided by DFT calculations, which were also employed to study the electronic structure of the compound

Insights into Hydrate Formation and Stability of Morphinanes from a Combination of Experimental and Computational Approaches

Morphine, codeine, and ethylmorphine are important drug compounds whose free bases and hydrochloride salts form stable hydrates. These compounds were used to systematically investigate the influence of the type of functional groups, the role of water molecules, and the Cl^– counterion on molecular aggregation and solid state properties. Five new crystal structures have been determined. Additionally, structure models for anhydrous ethylmorphine and morphine hydrochloride dihydrate, two phases existing only in a very limited humidity range, are proposed on the basis of computational dehydration modeling. These match the experimental powder X-ray diffraction patterns and the structural information derived from infrared spectroscopy. All 12 structurally characterized morphinane forms (including structures from the Cambridge Structural Database) crystallize in the orthorhombic space group <i>P</i>2₁2₁2₁. Hydrate formation results in higher dimensional hydrogen bond networks. The salt structures of the different compounds exhibit only little structural variation. Anhydrous polymorphs were detected for all compounds except ethylmorphine (one anhydrate) and its hydrochloride salt (no anhydrate). Morphine HCl forms a trihydrate and dihydrate. Differential scanning and isothermal calorimetry were employed to estimate the heat of the hydrate ↔ anhydrate phase transformations, indicating an enthalpic stabilization of the respective hydrate of 5.7 to 25.6 kJ mol^–1 relative to the most stable anhydrate. These results are in qualitative agreement with static 0 K lattice energy calculations for all systems except morphine hydrochloride, showing the need for further improvements in quantitative thermodynamic prediction of hydrates having water···water interactions. Thus, the combination of a variety of experimental techniques, covering temperature- and moisture-dependent stability, and computational modeling allowed us to generate sufficient kinetic, thermodynamic and structural information to understand the principles of hydrate formation of the model compounds. This approach also led to the detection of several new crystal forms of the investigated morphinanes

Synthesis and Characterization of Single Crystal Zircon-Hafnon Zr_{(1–<i>x</i>)}Hf_(<i>x</i>)SiO₄ Solid Solutions and the Comparison with the Reaction Products of a TEOS-Based Hydrothermal Route

Two synthesis routes of the zircon–hafnon solid solution series were carried out. The high-temperature route uses the growth of single crystals via a flux mixture that has been cooled down slowly from 1400 °C over 4 weeks. The reaction products were colorless and idiomorphic without byproducts. The hydrothermal tetraethoxysilane (TEOS)-based route represents the low-temperature method at 200 °C for approximately 7 days. The hydrothermal route yielded a white powder and scanning electron microscopy analysis thereof did not reveal any specific idiomorphic properties. However, the synthesis also featured some byproducts besides the zircon–hafnon solid solutions. Thermogravimetric analysis coupled with differential scanning calorimetry, and mass spectroscopy indicated, that hydrothermal reaction products feature the presence of organic residues originating from the starting materials. However, a specific dependency on the hafnium content could not be observed due to the data scatter. Infrared (IR) analysis revealed the presence of Zr/Hf-oxides. The structural characterization demonstrated that properties change constantly with the hafnium amount, however, gradual variations of some properties related to the composition of the solid solution series depend in part on the synthesis route, considering the c/a ratio and IR modes. Furthermore, analyses of the single crystals by Raman spectroscopy and μXRF suggested a nonequilibrated crystal growth based on the starting composition

Crystallization of Metastable Polymorphs of Phenobarbital by Isomorphic Seeding

Six metastable polymorphs (V, VII−XI) of phenobarbital (Pbtl) were produced by melt crystallization via seeding with corresponding isomorphic barbiturate homologues, following the teachings of earlier thermoanalytical studies of isopolymorphic relationships and utilizing the melting phase diagrams of Pbtl admixtures with various 5,5-substituted barbituric acid derivatives. The Pbtl forms and their solid solutions were analyzed with hot-stage microscopy, powder X-ray diffraction, and infrared spectroscopy. The crystal structures of several isomorphic homologues were determined to assess the structural features of the metastable Pbtl polymorphs. In contrast to Pbtl-V, VIII, and IX, which could be isolated as a single component phase, Pbtl-VII, X, and XI could only be stabilized in the presence of one of the isomorphic additives. Form Pbtl-V, the most stable form among the six metastable polymorphs, is structurally similar to Pbtl-IV and was crystallized by seeding with co-crystals of Pbtl/rutonal (3:1). Pbtl-VII was obtained as a stabilized intermediate phase from the system dipropylbarbital/Pbtl. Pbtl-VIII occurs on seeding with alphenal (Alp) form I. The structure analysis of this orthorhombic Alp modification revealed the presence of N−H···OC hydrogen bonded layers. Pbtl-IX and X show isomorphic relationships to a rich variety of different barbiturate structures, all based on the same pair of H-bonded ribbon chains. The packing features of Pbtl-IX were deduced from the isomorphic structures of amytal-II and soneryl-I. Pbtl-X is isomorphic to both amytal-I and phanodorm-II. The existence of form XI was confirmed via the solid solutions of Pbtl/Alp and Pbtl/dipropylbarbital. This study conveys some of the basic principles of isomorphic additives on the formation of specific polymorphs or the stabilization of unstable crystal forms, which are not detectable in solvent or melt crystallization experiments of the pure compound

Synthesis and Characterization of Single Crystal Zircon-Hafnon Zr_{(1–<i>x</i>)}Hf_(<i>x</i>)SiO₄ Solid Solutions and the Comparison with the Reaction Products of a TEOS-Based Hydrothermal Route

Two synthesis routes of the zircon–hafnon solid solution series were carried out. The high-temperature route uses the growth of single crystals via a flux mixture that has been cooled down slowly from 1400 °C over 4 weeks. The reaction products were colorless and idiomorphic without byproducts. The hydrothermal tetraethoxysilane (TEOS)-based route represents the low-temperature method at 200 °C for approximately 7 days. The hydrothermal route yielded a white powder and scanning electron microscopy analysis thereof did not reveal any specific idiomorphic properties. However, the synthesis also featured some byproducts besides the zircon–hafnon solid solutions. Thermogravimetric analysis coupled with differential scanning calorimetry, and mass spectroscopy indicated, that hydrothermal reaction products feature the presence of organic residues originating from the starting materials. However, a specific dependency on the hafnium content could not be observed due to the data scatter. Infrared (IR) analysis revealed the presence of Zr/Hf-oxides. The structural characterization demonstrated that properties change constantly with the hafnium amount, however, gradual variations of some properties related to the composition of the solid solution series depend in part on the synthesis route, considering the c/a ratio and IR modes. Furthermore, analyses of the single crystals by Raman spectroscopy and μXRF suggested a nonequilibrated crystal growth based on the starting composition

Expanding the Solid Form Landscape of Bipyridines

Two bipyridine isomers (2,2′- and 4,4′-), used as coformers and ligands in coordination chemistry, were subjected to solid form screening and crystal structure prediction. One anhydrate and a formic acid disolvate were crystallized for 2,2′-bipyridine, whereas multiple solid-state forms, anhydrate, dihydrate, and eight solvates with carboxylic acids, including a polymorphic acetic acid disolvate, were found for the 4,4′-isomer. Seven of the solvates are reported for the first time, and structural information is provided for six of the new solvates. All twelve solid-state forms were investigated comprehensively using experimental [thermal analysis, isothermal calorimetry, X-ray diffraction, gravimetric moisture (de)­sorption, and IR spectroscopy] and computational approaches. Lattice and interaction energy calculations confirmed the thermodynamic driving force for disolvate formation, mediated by the absence of H-bond donor groups of the host molecules. The exposed location of the N atoms in 4,4′-bipyridine facilitates the accommodation of bigger carboxylic acids and leads to higher conformational flexibility compared to 2,2′-bipyridine. For the 4,4′-bipyridine anhydrate ↔ hydrate interconversion hardly any hysteresis and a fast transformation kinetics are observed, with the critical relative humidity being at 35% at room temperature. The computed anhydrate crystal energy landscapes have the 2,2′-bipyridine as the lowest energy structure and the 4,4′-bipyridine among the low-energy structures and suggest a different crystallization behavior of the two compounds

Synthesis and Characterization of Single Crystal Zircon-Hafnon Zr_{(1–<i>x</i>)}Hf_(<i>x</i>)SiO₄ Solid Solutions and the Comparison with the Reaction Products of a TEOS-Based Hydrothermal Route

Two synthesis routes of the zircon–hafnon solid solution series were carried out. The high-temperature route uses the growth of single crystals via a flux mixture that has been cooled down slowly from 1400 °C over 4 weeks. The reaction products were colorless and idiomorphic without byproducts. The hydrothermal tetraethoxysilane (TEOS)-based route represents the low-temperature method at 200 °C for approximately 7 days. The hydrothermal route yielded a white powder and scanning electron microscopy analysis thereof did not reveal any specific idiomorphic properties. However, the synthesis also featured some byproducts besides the zircon–hafnon solid solutions. Thermogravimetric analysis coupled with differential scanning calorimetry, and mass spectroscopy indicated, that hydrothermal reaction products feature the presence of organic residues originating from the starting materials. However, a specific dependency on the hafnium content could not be observed due to the data scatter. Infrared (IR) analysis revealed the presence of Zr/Hf-oxides. The structural characterization demonstrated that properties change constantly with the hafnium amount, however, gradual variations of some properties related to the composition of the solid solution series depend in part on the synthesis route, considering the c/a ratio and IR modes. Furthermore, analyses of the single crystals by Raman spectroscopy and μXRF suggested a nonequilibrated crystal growth based on the starting composition

The Homoleptic Square-Antiprismatic Chelate Tetrakis(3-acetyl-2,4-pentanedionato)zirconium(IV): A Promising Coordination Motif for Tetrahedral Metal−Organic Frameworks

The novel analogue of the parent Zr(acac)4 complex, tetrakis(3-acetyl-2,4-pentanedionato)zirconium(IV), Zr[C7O3H9]4, has been synthesized straightforwardly by a salt-free methodology and was characterized by a number of complementary methods (1H NMR, 13C NMR, IR, and bulk density). From polycrystalline material, X-ray powder diffractograms and micro-Raman spectra were obtained and are discussed in detail. The crystal structure was determined from laboratory X-ray powder diffraction data by simulated annealing and subsequently refined with the Rietveld technique. The compound is monoclinic with space group P2/c. Zr, residing on a crystallographic 2-fold rotation axis, is coordinated by the four chelating ligands forming a square-antiprismatic coordination polyhedron. Differences and similarities to zirconium(IV)acetylacetonate, Zr[C5O2H7]4, and other similar complexes are discussed, addressing the conformational rigidity of this symmetrically substituted homoleptic acac complex

Insights into Hydrate Formation and Stability of Morphinanes from a Combination of Experimental and Computational Approaches

Morphine, codeine, and ethylmorphine are important drug compounds whose free bases and hydrochloride salts form stable hydrates. These compounds were used to systematically investigate the influence of the type of functional groups, the role of water molecules, and the Cl^– counterion on molecular aggregation and solid state properties. Five new crystal structures have been determined. Additionally, structure models for anhydrous ethylmorphine and morphine hydrochloride dihydrate, two phases existing only in a very limited humidity range, are proposed on the basis of computational dehydration modeling. These match the experimental powder X-ray diffraction patterns and the structural information derived from infrared spectroscopy. All 12 structurally characterized morphinane forms (including structures from the Cambridge Structural Database) crystallize in the orthorhombic space group <i>P</i>2₁2₁2₁. Hydrate formation results in higher dimensional hydrogen bond networks. The salt structures of the different compounds exhibit only little structural variation. Anhydrous polymorphs were detected for all compounds except ethylmorphine (one anhydrate) and its hydrochloride salt (no anhydrate). Morphine HCl forms a trihydrate and dihydrate. Differential scanning and isothermal calorimetry were employed to estimate the heat of the hydrate ↔ anhydrate phase transformations, indicating an enthalpic stabilization of the respective hydrate of 5.7 to 25.6 kJ mol^–1 relative to the most stable anhydrate. These results are in qualitative agreement with static 0 K lattice energy calculations for all systems except morphine hydrochloride, showing the need for further improvements in quantitative thermodynamic prediction of hydrates having water···water interactions. Thus, the combination of a variety of experimental techniques, covering temperature- and moisture-dependent stability, and computational modeling allowed us to generate sufficient kinetic, thermodynamic and structural information to understand the principles of hydrate formation of the model compounds. This approach also led to the detection of several new crystal forms of the investigated morphinanes