Alkali metal hydride complexes: well-defined molecular species of saline hydrides

The first examples of well-defined alkali metal hydride complexes have been synthesised and characterised in recent years, and their properties and underlying principles for their generation and stabilisation are emerging. This article gives an account of the hydrides of the alkali metals (Group 1 metals) and selected ‘-ate’ complexes containing hydrides and alkali metals, and reviews the chemistry of well-defined alkali metal hydride complexes including their syntheses, structures, and characteristics. The properties of the alkali metal hydrides LiH, NaH, KH, RbH, and CsH are dominated by their ionic NaCl structure. Stable, soluble, and well-defined LiH and NaH complexes have been obtained by metathesis and β-hydride elimination reactions that require suitable ligands with some steric bulk and the ability to coordinate to several metal ions. These novel hydride complexes reward with higher reactivity and different properties compared with their parent ionic solids.