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Tetrafluoroberyllate
Tetrafluoroberyllate or orthofluoroberyllate is an anion with the chemical formula [BeF4]2−. It contains beryllium and fluorine. This fluoroanion has a tetrahedral shape, with the four fluorine atoms surrounding a central beryllium atom. It has the same size, charge, and outer electron structure as sulfate SO2−4. Therefore, many compounds that contain sulfate have equivalents with tetrafluoroberyllate. Examples of these are the langbeinites, and Tutton's salts.
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. In trifluoroberyllates, there are actually BeF4 tetrahedra arranged in a triangle, so that three fluorine atoms are shared on two tetrahedra each, resulting in a formula of Be3F9.
In the tetrafluoroberyllates, the tetrahedra can rotate to various degrees. At room temperature, they are hindered from moving. But as temperature increases, they can rotate around the threefold axis, (i.e. a line through one fluorine atom and the beryllium atom) with a potential barrier of 12.5 kcal/mol (52 kJ/mol). At higher temperatures, the movement can become isotropic (not limited to rotation on one axis) with a potential barrier of 14.5 kcal/mol (61 kJ/mol).
Similar compounds have magnesium or zinc in a similar position as beryllium, e.g. K2[MgF4] (potassium tetrafluoromagnesate) or [NH4]2[ZnF4] (ammonium tetrafluorozincate) but these are not as stable.
Tetrafluoroberyllate has a biological effect by inhibiting F-ATPase adenosine triphosphate producing enzymes in mitochondria and bacteria. It does this by attempting to react with adenosine diphosphate because it resembles phosphate. However once it does this it remains stuck in the F1 part of the enzyme and inhibits it from further function.
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. The gas above molten sodium tetrafluoroberyllate contains BeF2 and NaF gas.
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. Li2BeF4 can be crystallised from aqueous solution using (NH4)2BeF4 and LiCl.
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 can be used as a starting point to make the non-linear optic crystal KBe2BO3F2 which has the highest power handling capacity and shortest UV performance of any borate. It is quite soluble in water, so beryllium can be extracted from soil in this form.
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Tetrafluoroberyllate
Tetrafluoroberyllate or orthofluoroberyllate is an anion with the chemical formula [BeF4]2−. It contains beryllium and fluorine. This fluoroanion has a tetrahedral shape, with the four fluorine atoms surrounding a central beryllium atom. It has the same size, charge, and outer electron structure as sulfate SO2−4. Therefore, many compounds that contain sulfate have equivalents with tetrafluoroberyllate. Examples of these are the langbeinites, and Tutton's salts.
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. In trifluoroberyllates, there are actually BeF4 tetrahedra arranged in a triangle, so that three fluorine atoms are shared on two tetrahedra each, resulting in a formula of Be3F9.
In the tetrafluoroberyllates, the tetrahedra can rotate to various degrees. At room temperature, they are hindered from moving. But as temperature increases, they can rotate around the threefold axis, (i.e. a line through one fluorine atom and the beryllium atom) with a potential barrier of 12.5 kcal/mol (52 kJ/mol). At higher temperatures, the movement can become isotropic (not limited to rotation on one axis) with a potential barrier of 14.5 kcal/mol (61 kJ/mol).
Similar compounds have magnesium or zinc in a similar position as beryllium, e.g. K2[MgF4] (potassium tetrafluoromagnesate) or [NH4]2[ZnF4] (ammonium tetrafluorozincate) but these are not as stable.
Tetrafluoroberyllate has a biological effect by inhibiting F-ATPase adenosine triphosphate producing enzymes in mitochondria and bacteria. It does this by attempting to react with adenosine diphosphate because it resembles phosphate. However once it does this it remains stuck in the F1 part of the enzyme and inhibits it from further function.
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. The gas above molten sodium tetrafluoroberyllate contains BeF2 and NaF gas.
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. Li2BeF4 can be crystallised from aqueous solution using (NH4)2BeF4 and LiCl.
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 can be used as a starting point to make the non-linear optic crystal KBe2BO3F2 which has the highest power handling capacity and shortest UV performance of any borate. It is quite soluble in water, so beryllium can be extracted from soil in this form.