Tetrafluoroberyllate

The Be–F bond length is between 145 and 153 pm. The beryllium is sp3 hybridized, leading to a longer bond than in BeF2|, where beryllium is sp hybridized. ==Simple salts==

Sodium tetrafluoroberyllate has several crystalline forms. Below 220 °C it takes the same form as orthorhombic olivine, and this is called γ phase. Between 220 °C and 320 °C it is in the α′ form. When temperature is raised above 320 °C it changes to the hexagonal α form. When cooled the α′ form changes to β form at 110 °C and this can be cooled to 70 °C before changing back to the γ form. It can be formed by melting sodium fluoride and beryllium fluoride. Lithium tetrafluoroberyllate takes on the same crystal form as the mineral phenacite. As a liquid it is proposed for the molten salt reactor, in which it is called FLiBe. The liquid salt has a high specific heat, similar to that of water. The molten salt has a very similar density to the solid. The solid has continuous void channels through it, which reduces its density. Potassium tetrafluoroberyllate has the same structure as anhydrous potassium sulfate, as does rubidium and caesium tetrafluoroberyllate. Potassium tetrafluoroberyllate can make solid solutions with potassium sulfate. It is quite soluble in water, so beryllium can be extracted from soil in this form. Ammonium tetrafluoroberyllate decomposes on heating by losing vapour, progressively forming , then and finally . Radium tetrafluoroberyllate is used as a standard neutron source. The alpha particles from the radium cause neutrons to be emitted from the beryllium. It is precipitated from a radium chloride solution mixed with potassium tetrafluoroberyllate. Calcium tetrafluoroberyllate resembles zircon in the way it melts and crystallises. The crystals can be formed by dissolving in water, adding HF and then glycine. When the solution is cooled triglycine tetrafluoroberyllate forms. and in the solution reduce growth on the 001 direction so that tabular shaped crystals of TGFB form. The thallium compound can cut growth on the 001 axis by 99%. ==Double salts==

Tuttons salts The Tuttons salt (NH4)2Mn(BeF4)2·6(H2O) is made from a solution of NH4BeF3 mixed with NH4MnF3. Tutton's salts (also called schoenites) containing magnesium with fluoroberyllate are difficult to produce, as the solutions tend to precipitate insoluble MgF2. Alums Tetrafluoroberyllate salts equivalent to alums also exist with formula MABF4·12H2O, where M is univalent, and A trivalent. These are not common as fluoride often form insoluble products with the trivalent ions. Methods to produce these include evaporating mixed fluoride solutions under reduced pressure at 0 °C, or dissolving beryllium and other metal hydroxides in hydrofluoric acid at room temperature, cooled, and them mixing with cold ethyl alcohol, causing cooling and crystallisation. The unit cell dimensions are slightly smaller (by 0.03–0.05 Å) than the corresponding sulfate alums. ==References==