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Caroline Mellot-Draznieks

Publications and source records attributed to Caroline Mellot-Draznieks.

12 recordsLinked to original sources
PubMed2006

The first route to large pore metal phosphonates.

The first large pore (free diameter > 7 A) metal phosphonates have been prepared as divalent metal N,N'-piperazinebis(methylenephosphonate)s that possess pores greater than ca. 10 A in free diameter, are stable up to 400 degrees C and offer a route to chiral adsorbents and catalysts.

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PubMed2005

A new isoreticular class of metal-organic-frameworks with the MIL-88 topology.

We report here a new family of isoreticular MOFs, comprising three larger analogues of the nanoporous metallocarboxylate MIL-88; these solids were synthesized using a controlled SBU approach and the three crystal structures were solved using an original simulation-assisted structure determination method in direct space.

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PubMed2005

Very large swelling in hybrid frameworks: a combined computational and powder diffraction study.

Using a combination of simulations and powder diffraction, we report here the study of the very large swelling of a three-dimensional nanoporous iron(III) carboxylate (MIL-88) which exhibits almost a reversible doubling (approximately 85%) of its cell volume while fully retaining its open-framework topology. The crystal structure of the open form of MIL-88 has been successfully refined and indicates that atomic displacements larger than 4 angstroms are observed when water or various alcohols are adsorbed in the porous structure, revealing an unusually flexible crystallized framework. X-ray thermodiffractometry shows that only a displacive transition occurs during the swelling phenomenon, ruling out any bond breaking.

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PubMed2005

Crystallized frameworks with giant pores: are there limits to the possible?

In the domain of porous solids with inorganic or hybrid frameworks, the combination of mastered chemistry and of computer simulations pushes forward the limits of the classical approach and allows the full determination from powder diffraction data of architectures with cells of several hundred thousand cubic angstroms with hierarchies of giant pores and unprecedented Langmuir surfaces. The different limits induced by this new approach are analyzed.

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PubMed2002

Novel inorganic frameworks constructed from double-four-ring (D4R) units: computational design, structures, and lattice energies of silicate, aluminophosphate, and gallophosphate candidates.

The design of new and interesting inorganic frameworks is an ongoing challenge in materials sciences. New structures containing double-four-ring (D4R) units have recently received particular attention. The present work focuses on the computational design of new three-dimensional frameworks made of D4R units exclusively. In a first step, our simulations explore the possible ways to assemble predefined D4R units in 3D space using a sophisticated cascade of simulated annealing/minimizations steps (autoassembly of secondary building units method). While the existing zeotype topologies were successfully generated, new topologies were predicted including very open frameworks containing new types of cages. In a second step, lattice energy minimizations were performed to estimate the viability of these hypothetical frameworks as silicate, aluminophosphaste, and gallophosphate candidates. When comparing the hypothetical structures to existing compounds, our results raise the challenging question of the appropriate chemical composition that should be aimed at for a given framework topology of interest.

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PubMed2002

Computational design and prediction of interesting not-yet-synthesized structures of inorganic materials by using building unit concepts.

The computational design of new and interesting inorganic materials is still an ongoing challenge. The motivation of these efforts is to aid the often difficult task of crystal structure determination, to rationalize different but related structure types, or to help limit the domain of structures that are possible in a given system. Over the past decade, simulation methods have continuously evolved towards the prediction of new structures using minimal input information in terms of symmetry, cell parameters, or chemical composition. So far, this task of identifying candidate structures through an analysis of the energy landscape of chemical systems has been particularly successful for predominantly ionic systems with relatively small numbers of atoms or ions in the simulation cell. After an introductory section, the second section of this work presents the historical developments of such simulation methods in this area. The following sections of the work are dedicated to the introduction of the building unit concept in simulation methods: we present simulation approaches to structure prediction employing both primary (aggregate of atoms) and secondary (aggregate of coordination polyhedra) building units. While structure prediction with primary units is a straightforward extension of established approaches, the AASBU method (automated asssembly of secondary building units) focusses on the topology of network-based structures. This method explores the possible ways to assemble predefined inorganic building units in three-dimensional space, opening the way to the manipulation of very large building units (up to 84 atoms in this work). As illustrative examples we present the prediction of candidate structures for Li(4)CO(4), the identification of topological relationships within a family of metalphosphates, ULM-n and MIL-n, and finally the generation of new topologies by using predefined large building units such as a sodalite or a double-four-ring cage, for the prediction of new and interesting zeolite-type structures.

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PubMed2002

Framework stability of nanoporous inorganic structures upon template extraction and calcination: a theoretical study of gallophosphate polymorphs.

A systematic computational study of gallophosphates was undertaken. First, lattice energy minimization calculations using a formal-charge shell model potential have been carried out on a series of hypothetical gallium phosphates derived from their metallogallophosphate, aluminophosphate, or aluminosilicate analogues through atomic substitution. The minimized structures show the typical features in terms of bond angles and distances as expected in zeolitic gallophosphates. Second, the crystal structures of several gallophosphates in their calcined forms have been predicted, using for each compound lattice energy minimization and an initial model derived from its as-synthesized templated form. All the modified structures thus have the same GaPO(4) composition. The lattice energies of all the simulated gallophosphate structures were compared to that of GaPO(4)-quartz as a reference structure. Interestingly, among all predicted calcined structures, various zeolitic topologies were found. The study of the energetics of these zeotypic structures showed a linear dependence of lattice energy upon density. Strikingly, a few simulated structures showed unrealistic structural features, such as important framework distortions, often associated with the occurrence of a hexameric unit in the original as-synthesized structures. Also, those gallophosphates with structural faults were found in the upper part of the energy/density plot. To address the validity of our force field calculations in these special cases, first principles calculations were undertaken on ULM-4, chosen as a typical representative structure. Indeed, the qualitative agreement found between our results and those obtained with the nonlocal density functional theory demonstrates the robustness of our force field. Further minimization also showed that the inclusion of polarizability is crucial for yielding results comparable with those obtained using first principles methods.

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