Furosemide Cocrystals: Structures, Hydrogen Bonding, and Implications for Properties

In this paper, we report the crystal growth of four cocrystals of furosemide (4-chloro-2-[(2-furanylmethyl)­amino]-5-sulfamoylbenzoic acid), a loop diuretic drug used for the treatment of hypertension and edemas, prepared with <i>p</i>-aminobenzoic acid, nicotinamide, and isonicotinamide as coformers. We present four new crystal structures and elucidate the intermolecular interactions present in the cocrystals. The structures display interesting supramolecular chemistry: a number of different synthons, as well as short strong hydrogen bonds with partial proton transfer and indications of proton disorder. Using powder X-ray diffraction, solid state NMR, and thermal analysis, we provide evidence for the preparation of bulk samples of two compositions, namely, the 1:1 cocrystal of furosemide and <i>p</i>-aminobenzoic acid and 2:1 cocrystal of furosemide and isonicotinamide, highlighting the general necessity of such multitechnique approaches to characterize organic solids (including cocrystals and solvates) prepared by grinding methods. Finally, we correlate the structural features reported for the first time in this work with the previously published pharmacologically relevant properties (solubility and intrinsic dissolution rate) of the furosemide cocrystals

On Sr_1–<i>x</i>Na_<i>x</i>SiO_{3–0.5<i>x</i>} New Superior Fast Ion Conductors

On Sr_1–<i>x</i>Na_<i>x</i>SiO_{3–0.5<i>x</i>} New Superior Fast Ion Conductor

Polymorphism and Oxide Ion Migration Pathways in Fluorite-Type Bismuth Vanadate, Bi₄₆V₈O₈₉

We report the synthesis, structural characterization, and ionic conductivity measurements for a new polymorph of bismuth vanadate Bi₄₆V₈O₈₉, and an <i>ab initio</i> molecular dynamics study of this oxide ion conductor. Structure determination was carried out using synchrotron powder X-ray and neutron diffraction data; it was found that β-Bi₄₆V₈O₈₉ crystallizes in space group <i>C</i>2/<i>m</i> and that the key differences between this and the previously reported α-form are the distribution of Bi and V cations and the arrangement of the VO₄ coordination polyhedra in structure. β-Bi₄₆V₈O₈₉ exhibits good oxide ion conductivity, with σ = 0.01–0.1 S/cm between 600 and 850 °C, which is about an order of magnitude higher than yttria stabilized zirconia. The <i>ab initio</i> molecular dynamics simulations suggest that the ion migration pathways include vacancy diffusion through the Bi–O sublattice, as well as the O^2– exchanges between the Bi–O and the V–O sublattices, facilitated by the variability of the vanadium coordination environment and the rotational freedom of the VO_<i>x</i> coordination polyhedra

Polymorphism and Oxide Ion Migration Pathways in Fluorite-Type Bismuth Vanadate, Bi₄₆V₈O₈₉

We report the synthesis, structural characterization, and ionic conductivity measurements for a new polymorph of bismuth vanadate Bi₄₆V₈O₈₉, and an <i>ab initio</i> molecular dynamics study of this oxide ion conductor. Structure determination was carried out using synchrotron powder X-ray and neutron diffraction data; it was found that β-Bi₄₆V₈O₈₉ crystallizes in space group <i>C</i>2/<i>m</i> and that the key differences between this and the previously reported α-form are the distribution of Bi and V cations and the arrangement of the VO₄ coordination polyhedra in structure. β-Bi₄₆V₈O₈₉ exhibits good oxide ion conductivity, with σ = 0.01–0.1 S/cm between 600 and 850 °C, which is about an order of magnitude higher than yttria stabilized zirconia. The <i>ab initio</i> molecular dynamics simulations suggest that the ion migration pathways include vacancy diffusion through the Bi–O sublattice, as well as the O^2– exchanges between the Bi–O and the V–O sublattices, facilitated by the variability of the vanadium coordination environment and the rotational freedom of the VO_<i>x</i> coordination polyhedra

An Exhaustive Symmetry Approach to Structure Determination: Phase Transitions in Bi₂Sn₂O₇

The exploitable properties of many materials are intimately linked to symmetry-lowering structural phase transitions. We present an automated and exhaustive symmetry-mode method for systematically exploring and solving such structures which will be widely applicable to a range of functional materials. We exemplify the method with an investigation of the Bi₂Sn₂O₇ pyrochlore, which has been shown to undergo transitions from a parent γ cubic phase to β and α structures on cooling. The results include the first reliable structural model for β-Bi₂Sn₂O₇ (orthorhombic <i>Aba</i>2, <i>a</i> = 7.571833(8), <i>b</i> = 21.41262(2), and <i>c</i> = 15.132459(14) Å) and a much simpler description of α-Bi₂Sn₂O₇ (monoclinic <i>Cc</i>, <i>a</i> = 13.15493(6), <i>b</i> = 7.54118(4), and <i>c</i> = 15.07672(7) Å, β = 125.0120(3)°) than has been presented previously. We use the symmetry-mode basis to describe the phase transition in terms of coupled rotations of the Bi₂O′ anti-cristobalite framework, which allow Bi atoms to adopt low-symmetry coordination environments favored by lone-pair cations

Direct Observation of Oxide Ion Dynamics in La₂Mo₂O₉ on the Nanosecond Timescale

Quasielastic neutron scattering (QENS), underpinned by ab initio molecular dynamics (AIMD) simulations, has been used to directly observe oxide ion dynamics in solid electrolyte La₂Mo₂O₉ on the nanosecond timescale, the longest timescale probed in oxide ion conductors by neutron scattering to date. QENS gives the activation energy of 0.61(5) eV for this process, while AIMD simulations reveal that the exchange processes, which ultimately lead to long-range oxide ion diffusion in La₂Mo₂O₉, rely on the flexibility of the coordination environment around Mo⁶⁺, with oxide ions jumps occurring between vacant sites both within and between Mo coordination spheres. Simulations also differentiate between the crystallographic sites which participate in the oxide ion exchange processes, offering the first atomic-level understanding of the oxide ion dynamics in La₂Mo₂O₉, which is consistent with the macroscopic experimental observations on this material