3-Dimensional Methylammonium and Ammonium Templated Lithiumberyllofluoro Frameworks

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.