Nanostructures in Uranium Oxocompounds
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Nanostructures in Uranium Oxocompounds Sergey V. Krivovichev, Ivan G. Tananaev1 and Boris F. Myasoedov1 Department of Crystallography, St.Petersburg State University, St.Petersburg 199034, Russia 1 Institute of Physical Chemistry, Russian Academy of Sciences, Leninsky pr. 31, Moscow, 119991, Russia ABSTRACT Examples of uranium-oxide-based nanostructures are considered, including 2D organicinorganic nanocomposites and nanotubules. In nanocomposites, interfacial interactions between organic and inorganic substructures can be studied by charge-density matching principle. Application of this principle to uranyl compounds requires special attention since surface area of uranyl-based 2D units is higher than that of other inorganic oxysalts units (i.e. metal phosphates). The charge-density matching principle is, however, observed either through tail interdigitation (for long-chain monoamines) or incorporation of acid-water interlayers into organic substructure (for long-chain diamines). In some compounds, protonated amine molecules form cylindrical micelles that involves self-assembly governed by competing hydrophobic/hydrophillic interactions. The flexible inorganic complexes present in the reaction mixture could then form around cylindrical micelles to produce highly undulated 2D sheets or nanotubules.
INTRODUCTION Nanotechnology is the term generaly used to describe the creation and exploitation of materials with at least one dimension in the nanometer range (1-1000 nm). These include nanocrystals and clusters (quantum dots), nanowires, nanotubes, thin films and superlattices (3Dimensional structures) [1,2]. Usually, nanostructures have more reactive surfaces and exhibit new functions for the same chemical composition. Investigations of organization of matter at the nano-level are under way in many chemical systems with present and potential applications in nanotechnology. Recently, nanoscale structures were reported for the first time for actinidecontaining compounds as well [3-6]. As it is well-known, solid-state chemistry of inorganic oxocompounds of hexa-, penta- and heptavalent actinide ions (An) is dominated by 2dimensional (2D) layered structures, due to the strong tendency of Anm+ cations to form linear actinyl ions, AnO2(m-4)+ [7,8]. The 2D character of polyhedra polymerization makes actinide oxocompounds attractive from the viewpoint of their potential ability to form nanostructures based upon real-2D and pseudo-2D topologies. For instance, spontaneous formation of nanotubes was observed in a number of systems where exfoliation of lamellar solids into individual sheets can be achieved. In this paper, we present our recent results on nanostructures in inorganic and organicinorganic uranyl selenates. This system is of special attraction for actinide chemistry since relatively soft synthetic conditions, on one hand, allow manipulations with many possible compositions, and, on the other hand, result in formation of highly ordered structures accessible via X-ray diffraction single-crystal structure
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