Complex metal hydride
Encyclopedia
Complex metal hydrides are salts wherein the anions contain hydride
s. In the older chemical literature as well as contemporary materials science textbooks, a "metal hydride" is assumed to be nonmolecular, i.e. three-dimensional lattices of atomic ions. In such systems, hydrides are often interstitial and nonstoichiometric, and the bonding between the metal and hydrogen atoms is significantly ionic. In contrast, complex metal hydrides typically contain more than one type of metal or metalloid and may be soluble but invariably react with water. They exhibit ionic bonding between a positive metal ion with molecular anions containing the hydride. In such materials the hydrogen is bonded with significant covalent character to the second metal or metalloid atoms.
, NaAlH4 (also known as sodium alanate), lithium aluminum hydride, LiAlH4, and lithium borohydride
, (LiBH4). Complex metal hydrides are often soluble in ether
ial solvent
s. Other complex metal hydrides are numerous. Illustrative examples include the salts [MgBr(THF
)2]4FeH6 and K2ReH9
.
Hydride
In chemistry, a hydride is the anion of hydrogen, H−, or, more commonly, a compound in which one or more hydrogen centres have nucleophilic, reducing, or basic properties. In compounds that are regarded as hydrides, hydrogen is bonded to a more electropositive element or group...
s. In the older chemical literature as well as contemporary materials science textbooks, a "metal hydride" is assumed to be nonmolecular, i.e. three-dimensional lattices of atomic ions. In such systems, hydrides are often interstitial and nonstoichiometric, and the bonding between the metal and hydrogen atoms is significantly ionic. In contrast, complex metal hydrides typically contain more than one type of metal or metalloid and may be soluble but invariably react with water. They exhibit ionic bonding between a positive metal ion with molecular anions containing the hydride. In such materials the hydrogen is bonded with significant covalent character to the second metal or metalloid atoms.
Examples
In general, complex metal hydrides have the formula MxM'yHn, where M is an alkali metal cation or cation complex and M' is a metal or metalloid. Well known examples feature group 13 elements, especially boron and aluminium including sodium aluminium hydrideSodium aluminium hydride
Sodium aluminium hydride or sodium alanate is a chemical compound used as a reducing agent. It is similar to lithium aluminium hydride....
, NaAlH4 (also known as sodium alanate), lithium aluminum hydride, LiAlH4, and lithium borohydride
Lithium borohydride
Lithium borohydride is a tetrahydroborate and known in organic synthesis as a reducing agent for esters. Although less common than the related sodium borohydride, the lithium salt offers some advantages of being highly soluble in ethers and being a stronger reducing agent but still safer to...
, (LiBH4). Complex metal hydrides are often soluble in ether
Ether
Ethers are a class of organic compounds that contain an ether group — an oxygen atom connected to two alkyl or aryl groups — of general formula R–O–R'. A typical example is the solvent and anesthetic diethyl ether, commonly referred to simply as "ether"...
ial solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
s. Other complex metal hydrides are numerous. Illustrative examples include the salts [MgBr(THF
ThF
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)2]4FeH6 and K2ReH9
Potassium nonahydridorhenate
Potassium nonahydridorhenate is an inorganic compound with the formula K2ReH9. This colourless salt features the ReH92− anion, a rare example of a coordination complex bearing only hydride ligands....
.