Exploring polymorphism and stoichiometric diversity in naproxen/proline cocrystals

We present naproxen/proline cocrystals discovered when combining enantiopure and racemic naproxen and proline. Using liquid-assisted grinding as the main method to explore the variety of crystal forms in this system, we found 17 cocrystals, of which the structures of only four of them were previously known. The naproxen/proline system exhibited multiple polymorphs of 1 : 1 stoichiometry as well as more rare cocrystals with 1 : 2 and 2 : 3 stoichiometries, two cocrystal hydrates and one cocrystal solvate. In situ ball-milling, used to monitor liquid-assisted grinding reactions, revealed that the solvent dictates the reaction intermediates even if the final reaction product stays the same. Synchrotron X-ray diffraction data collected in situ upon heating allowed us to monitor directly the phase changes upon heating and gave access to pure diffraction patterns of several cocrystals, thus enabling their structure determination from powder X-ray diffraction data; this method also confirmed the formation of a conglomerate in the RS-naproxen/DL-proline system. Proline in cocrystals kept its ability to form charge-assisted head-to-tail N–H⋯O hydrogen bonds, typical of pure crystalline amino acids, thus increasing the percentage of strong charge-assisted interactions in the structure and consequently providing some of the cocrystals with higher melting points as compared to pure naproxen. The majority of drugs are chiral, and hence, these data are of importance to the pharmaceutical industry as they provide insight into the challenges of chiral cocrystallization

Hybrid hydridic frameworks by the combination of complex hydrides and nitrogen-based organic ligands

Over the past 15 years, the research in hydrogen storage and the advances in powder diffraction techniques led to the discovery and structural characterization of numerous metal borohydride (M(BH4)) revealing bonding schemes similar to those of metal-organic-frameworks, the borohydride anion behaving as the linker. In this work, we combined metal borohydrides with neutral and negatively charged nitrogen-based organic ligands searching for hybrid compounds containing both the hydridic borohydride anion and the organic moiety in a single structure. This strategy was aiming at the formation of a new class of porous materials in which the organic part would provide the structural rigidity and the borohydride would provide the functionality. The focus was placed on the structural characterization of the compounds. Neutron powder diffraction and ab initio calculation were used to complement the synchrotron radiation X-ray powder diffraction data when the latter were not sufficient to build satisfactory structural models. Other techniques were used to probe the properties suggested by the structural features of the obtained materials. The compounds prepared showed that the structures are dominated by the interaction between the organic ligand and the metal, the borohydride group accommodating unfavorable coordination environments in some cases. This brings to the conclusion that despite its structure directing tendency, the borohydride group is not the suitable building block for the construction of porous hybrid compounds. However, this unfavorable environment leads to unprecedented rotational dynamics of the BH4 group with possible rotational tunneling.(SC - Sciences) -- UCL, 201

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Pour une réflexion collective sur l’enseignement de la géographie à l’Université

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Mixed-Metal Imidazolates Containing Alkali and Alkaline Earth Metals: Mechanochemical Synthesis and Crystal Structure of AMgIm3 (A = Na or K)

The first bimetallic imidazolates containing alkali and alkaline earth metals, NaMgIm3 and KMgIm3, respectively, are prepared by mechanochemical synthesis and are reported in this paper. NaMgIm3 has been prepared by the reaction between NaIm and Mg(BH4)2 as well as directly from NaIm and MgIm2. Structural evolution and thermal stability were followed by an in situ high-temperature X-ray powder diffraction experiment utilizing synchrotron radiation. In both compounds, the imidazolate ligand is connected to four metal cations forming a complex three-dimensional network with channels running along the c-direction. NaMgIm3 and KMgIm3 are the first members of a new family of imidazolate frameworks with stp topology. The formation of mixed-alkali-metal imidazolate compounds is thermodynamically controlled. LiIm and MgIm2 have not yielded a mixed-metal compound, while KIm reacts swiftly and forms KMgIm3