Sodium and Potassium Tetrahydridogallate

A solution of Li[GaH4] in diethyl ether is prepared by the standard methods,J1 and is stored in a needle-valve O-ring flask. The concentration of Li[GaH4]-ether solution is determined by hydrolysis of a known volume of the solution followed by gallium determination by ethylenediamine-tetraace-tic acid, disodium salt using copper-PAN [l-(2-pyridylazo)-2-naphthol copper complex] as the indicator.4 It is assumed that all the gallium is present as the tetrahydrogallate. Only an approximate concentration need be determined since an excess of sodium hydride or potassium hydride is used. 

Diethyl ether solutions of Li[GaH4] are converted to tetrahydrofuran (THF), monoglyme (dimethoxyethane), or diglyme solutions by adding an equal volume of the appropriate solvent to a diethyl ether solution in a Schlenk flask, and then removing the more volatile diethyl ether by vacuum distillation. In the case of THF, after the total volume of the solution has 

Both gallium hydride complexes are obtained as white, crystalline powders which remain white when stored at room temperature in the absence of air and moisture for periods in excess of one year. Their reaction with water is moderate when compared to the analogous aluminum hydride complexes. They undergo typical reactions for an [MH4] species, e.g., 

The sodium compound begins to decompose under an argon atmosphere at 165°, while the potassium compound begins to decompose at about 230°. Both of these compounds are considerably more stable than solid Li[GaH4] which is reported5 to lose hydrogen rapidly at 70°. 

Shriver, The Manipulation of Air-Sensitive Compounds, McGraw-Hill Book 

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