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Oxyhydride
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Oxyhydride
An oxyhydride is a mixed anion compound containing both oxide O2− and hydride ions H−. These compounds may be unexpected as the hydrogen and oxygen could be expected to react to form water. But if the metals making up the cations are electropositive enough, and the conditions are reducing enough, solid materials can be made that combine hydrogen and oxygen in the negative ion role.
The first oxyhydride to be discovered was lanthanum oxyhydride, a 1982 discovery. It was made by heating lanthanum oxide in an atmosphere of hydrogen at 900 °C. However, heating transition metal oxides with hydrogen usually results in water and the reduced metal.
Topochemical synthesis retains the basic structure of the parent compound, and only does the minimum rearrangements of atoms to convert to the final product. Topotactic transitions retain the original crystal symmetry. Reactions at lower temperatures do not distort the existing structure. Oxyhydrides in a topochemical synthesis can be produced by heating oxides with sodium hydride NaH or calcium hydride CaH2 at temperatures from 200–600 °C. TiH2 or LiH can also be used as an agent to introduce hydride. If calcium hydroxide or sodium hydroxide is formed, it might be able to be washed away. However for some starting oxides, this kind of hydride reduction might just yield an oxygen-deficient oxide.
Reactions under hot high-pressure hydrogen can result from heating hydrides with oxides. A suitable seal for the lid on the container is required, and one such substance is sodium chloride.
Oxyhydrides all contain an alkali metal, alkaline earth metal, or rare-earth element, which are needed in order to put electronic charge on hydrogen.
The hydrogen bonding in oxyhydrides can be covalent, metallic, and ionic bonding, depending on the metals present in the compound.
Oxyhydrides lose their hydrogen less than the pure metal hydrides.
The hydrogen in oxyhydrides is much more exchangeable. For example oxynitrides can be made at much lower temperatures by heating the oxyhydride in ammonia or nitrogen gas (say around 400 °C rather than 900 °C required for an oxide) Acidic attack can replace the hydrogen, for example moderate heating in hydrogen fluoride yields compounds containing oxide, fluoride, and hydride ions (oxyfluorohydride.) The hydrogen is more thermolabile, and can be lost by heating yielding a reduced valence metal compound.
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Oxyhydride
An oxyhydride is a mixed anion compound containing both oxide O2− and hydride ions H−. These compounds may be unexpected as the hydrogen and oxygen could be expected to react to form water. But if the metals making up the cations are electropositive enough, and the conditions are reducing enough, solid materials can be made that combine hydrogen and oxygen in the negative ion role.
The first oxyhydride to be discovered was lanthanum oxyhydride, a 1982 discovery. It was made by heating lanthanum oxide in an atmosphere of hydrogen at 900 °C. However, heating transition metal oxides with hydrogen usually results in water and the reduced metal.
Topochemical synthesis retains the basic structure of the parent compound, and only does the minimum rearrangements of atoms to convert to the final product. Topotactic transitions retain the original crystal symmetry. Reactions at lower temperatures do not distort the existing structure. Oxyhydrides in a topochemical synthesis can be produced by heating oxides with sodium hydride NaH or calcium hydride CaH2 at temperatures from 200–600 °C. TiH2 or LiH can also be used as an agent to introduce hydride. If calcium hydroxide or sodium hydroxide is formed, it might be able to be washed away. However for some starting oxides, this kind of hydride reduction might just yield an oxygen-deficient oxide.
Reactions under hot high-pressure hydrogen can result from heating hydrides with oxides. A suitable seal for the lid on the container is required, and one such substance is sodium chloride.
Oxyhydrides all contain an alkali metal, alkaline earth metal, or rare-earth element, which are needed in order to put electronic charge on hydrogen.
The hydrogen bonding in oxyhydrides can be covalent, metallic, and ionic bonding, depending on the metals present in the compound.
Oxyhydrides lose their hydrogen less than the pure metal hydrides.
The hydrogen in oxyhydrides is much more exchangeable. For example oxynitrides can be made at much lower temperatures by heating the oxyhydride in ammonia or nitrogen gas (say around 400 °C rather than 900 °C required for an oxide) Acidic attack can replace the hydrogen, for example moderate heating in hydrogen fluoride yields compounds containing oxide, fluoride, and hydride ions (oxyfluorohydride.) The hydrogen is more thermolabile, and can be lost by heating yielding a reduced valence metal compound.