Germyl, trihydridogermanate(1-), trihydrogermanide, trihydridogermyl or according to IUPAC Red Book: germanide is an anion containing germanium bounded with three hydrogens, with formula GeH−3. Germyl is the IUPAC term for the –GeH3 group. For less electropositive elements the bond can be considered covalent rather than ionic as "germanide" indicates. Germanide is the base for germane when it loses a proton.
GeH4 → GeH−3 + H+
The first germyl compound to be discovered was sodium germyl. Germane was reacted with sodium dissolved in liquid ammonia to produce sodium germyl. Other alkali metal germyl compounds are known. There are also numerous transition metal complexes that contain germyl as a ligand.
Formation
Alkali metal germyl compounds have been made by reacting germane with the alkali metal dissolved in liquid ammonia, or other non-reactive solvent.
Transition metal complexes cam be made by using lithium aluminium hydride to reduce a trichlorogermyl complex (−GeCl3), which in turn can be made from the transition metal complex chloride and GeCl2.
Salt elimination can be used in a reaction with monochlorogermane and a sodium salt of a transition metal anion:
GeClH3 + NaMn(CO)5 → NaCl + Mn(GeH3)(CO)5.
In the gas phase, the germyl anion GeH−3 can be made from germane by capturing an electron with more than 8eV of energy:
GeH4 + e− → GeH−3 + H•
The germyl radical can be produced and immobilised in molecular form by exposing germane to vacuum ultraviolet light in a solid argon matrix. On heating, digermane is formed:
2 GeH3• → GeH3GeH3
Properties
Germyl compounds react with water, so water cannot be used as a solvent. Liquids that have been used as solvents include liquid ammonia, ethyl amine, diglyme, or hexamethylphosphoramide. The choice of solvent depends on the temperature desired, whether alkali metals are going to be dissolved, whether the solvent needs to be distilled, and also if it reacts with the solute.
The bond between the metal ion and the germyl ion may be purely ionic, but may also be bonded via two bridging hydrogen atoms.
The energy to rip a hydrogen atom off germane to make the neutral radical is 82.0±2kcal/mol (343.1±8.4kJ/mol). GeH4 → GeH3• + H•. Electron affinity for the radical is 1.6eV: GeH3• + e− → GeH3−.
Gas phase acidity of germane is ΔG° acid is 350.8±1.3kcal/mol (1,467.7±5.4kJ/mol); ΔH° acid is 358.9kcal/mol (1,502kJ/mol) for GeH4 → GeH−3 + H+.
Both the anion GeH−3 and radical GeH• 3 have C3v symmetry, and are shaped as a triangular pyramid with germanium at the top, and three hydrogen atoms at the bottom. In the radical, the H-Ge-H angle is 110°. In the anion the H-Ge-H angle is about 93°.
Reactions
Germyl compounds gradually decompose at room temperature by releasing hydrogen and forming a metal germide.
12345678Kraus, Charles A.; Carney, E. Seaton (April 1934). "Compounds of Germanium and Hydrogen: Some of their Reactions and Derivatives. I. Preparation of Monogermane. II. Sodium Trihydrogermanides". Journal of the American Chemical Society. 56 (4): 765–768. Bibcode:1934JAChS..56..765K. doi:10.1021/ja01319a002.
↑Smith, George R.; Guillory, William A. (15 February 1972). "Products of the Vacuum-Ultraviolet Photolysis of Germane Isolated in an Argon Matrix". The Journal of Chemical Physics. 56 (4): 1423–1430. Bibcode:1972JChPh..56.1423S. doi:10.1063/1.1677383.
↑Cradock, Stephen; Gibbon, G. A.; Van Dyke, Charles H. (September 1967). "Germyl chemistry. V. Hexamethylphosphoramide as a solvent for the preparation and reaction of alkali metal derivatives of silane and germane". Inorganic Chemistry. 6 (9): 1751–1752. doi:10.1021/ic50055a034.
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