Magnesium hafnium tungstate [MgHf(WO4)3] was synthesized by high-energy ball milling followed by calcination. The material was characterized by variable- temperature neutron and x-ray diffraction. It crystallized in space group P21/a below 400 K and transformed to an orthorhombic structure at higher temperatures. The orthorhombic polymorph adopted space group Pnma, instead of the Pnca structure commonly observed for other A2(MO4)3 materials (A = trivalent metal, M = Mo, W). In contrast, the monoclinic polymorphs appeared to be isostructural. Negative thermal expansion was observed in the orthorhombic phase with αa = −5.2 × 10−6 K−1, αb = 4.4 × 10−6 K−1, αc = −2.9 × 10−6 K−1, αV = −3.7 × 10−6 K−1, and αl = −1.2 × 10−6 K−1. The monoclinic to orthorhombic phase transition was accompanied by a smooth change in unit-cell volume, indicative of a second-order phase transition.

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Advances in instrumentation, software applications, and database content have all contributed to improvements in pharmaceutical analyses by powder diffraction methods in the 21stcentury. When compared to the globally harmonized United States Pharmacopeia General Chapter <941>, “Characterization of Crystalline and Partially Crystalline Solids by X-ray Powder Diffraction”, many historic problems in pharmaceutical analysis have been addressed by combinations of improved methods and instrumentation. Major changes in the last 20 years include (i) a dramatic lowering in detection capability and detection limits, (ii) enhanced capabilities for dynamic measurements such asin situanalyses under a variety of conditions, and (iii) the ability to identify and characterize nanomaterials, non-crystalline, and amorphous materials by both coherent and incoherent scattering profiles.

The crystal structure of linagliptin hemihydrate hemiethanolate was solved by direct methods and refined by least-squares on the basis of 3D electron diffraction data. Linagliptin is one of the largest organic structures solved ab initio by electron diffraction. The good quality of the data allows the recognition of subtle symmetry reductions and of fine differences in the configuration of the two independent molecules that make up the structure. The structure was then further refined using synchrotron X-ray powder diffraction data and optimized using density functional techniques. The linagliptin hemihydrate hemiethanolate structure is very similar to the known linagliptin water/methanol/ethanol Form I, and crystallizes in space group P21212 (#18) with a = 24.85091(13), b = 21.56916(9), c = 9.74376(4) Å, V = 5222.79(3) Å3, and Z = 4. Although the compounds are similar, they are not the same, so the linagliptin hemihydrate hemiethanolate structure is a novel one. The powder pattern from a Le Bail fit to synchrotron data is included in the Powder Diffraction File as entry 00-066-1626.

A total pattern analysis suite of programs has been developed and incorporated into the ICDD® PDF-4 database. While the suite of programs is intended for the analysis of any diffraction pattern, particular attention was focused on the analysis of common amorphous, non-crystalline, or partially crystalline materials found in minerals, polymers, and pharmaceuticals. The suite of programs directly interfaces to the ICDD database and libraries of non-crystalline references.

The crystal structure of hydroxyzine dihydrochloride has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional techniques. Hydroxyzine dihydrochloride crystallizes in space group P21 (#4) with a = 11.48735(10), b = 7.41792(7), c = 14.99234(15) Å, β = 110.4383(10)°, V = 1197.107(13) Å3, and Z = 2. The hydroxyl-containing side chain of the cation is disordered over two conformations, with ~70/30% occupancy. The crystal structure consists of alternating polar (which includes the cation-anion interactions and hydrogen bonds) and nonpolar layers parallel to the ab-plane. The crystal structure is dominated by hydrogen bonds. Each of the protonated nitrogen atoms forms a very strong hydrogen bond to one of the chloride anions. The hydroxyl group forms a strong hydrogen bond to one of the chloride anions in both conformations, and there are subtle differences in the hydrogen bonding patterns between the conformations. The powder pattern is included in the Powder Diffraction File™ as entry 00-066-1603.

The crystal structure of hyoscyamine sulfate monohydrate has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional techniques. Hyoscyamine sulfate monohydrate crystallizes in space group P21 (#4) with a = 6.60196(2), b = 12.95496(3), c = 20.93090(8) Å, β = 94.8839(2)°, V = 1783.680(5) Å3, and Z = 2. Despite the traditional description as a dihydrate, hyoscyamine sulfate crystallizes as a monohydrate. The two independent hyoscyamine cations have different conformations, which have similar energies. One of the cations is close to the minimum-energy conformation. Each of the protonated nitrogen atoms in the cations acts as a donor to the sulfate anion. The hydroxyl group of one cation acts as a donor to the sulfate anion, while the hydroxyl group of the other cation acts as a donor to the water molecule. The water molecule acts as a donor to two different sulfate anions. The cations and anions are linked by complex chains of hydrogen bonds along the a-axis. The powder pattern has been submitted for inclusion in the Powder Diffraction File™ (PDF®).

The crystal structure of sitagliptin dihydrogen phosphate monohydrate (sometimes referred to as sitagliptin phosphate monohydrate) has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional techniques. Sitagliptin dihydrogen phosphate monohydrate crystallizes in space group P212121 (#19) with a = 6.137 108(12), b = 9.304 018(14), c = 38.307 67(10) Å, V = 2187.359(8) Å3, and Z = 4. The sitagliptin cation folds so that the two planar portions are roughly parallel. The ammonium group of the sitagliptin cation, the phosphate anion, and the water molecule form a network of strong hydrogen bonds. The result is a two-dimensional network, parallel to the ab plane. Halfway between these hydrogen bond planes, there are planes of high fluorine density. The powder pattern is included in the Powder Diffraction File™ as entry 00-064-1500.