American Chemical Society
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3-Dimensional Methylammonium and Ammonium Templated Lithiumberyllofluoro Frameworks

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journal contribution
posted on 2004-05-04, 00:00 authored by Lee A. Gerrard, Mark T. Weller
Two three-dimensional lithiumberyllofluoride materials, of the same framework stoichiometry but different topologies, have been synthesized using hydrothermal pressure conditions and ammonium/methylammonium cations as structure-directing species. Compound I, [Li2Be2F7][NH4], and compound II, [Li2Be2F7][CH3NH3], both crystallize in orthorhombic space groups:  Pca21 for I and Cmcm for II. Single crystal analysis reveals that the materials have slightly different 3-D framework topologies for the [Li2Be2F7] framework composed of [LiF4] and [BeF4] tetrahedra connected through doubly and triply bridging fluorides. Both networks can be viewed as sheets formed of 3- and 4-nets that link perpendicular to the sheet, through a bridging fluoride, to form six-membered interlayer pores. The six-membered channels contain the amine species hydrogen-bonded to framework fluoride ions surrounding the interior of the pore. The thermal stability, spectroscopic properties, and both powder X-ray and neutron data of these compounds are reported, along with the single-crystal analysis used to solve the structures.