Covalently bonded hydrides

Only limited comparisons can be made with the transition metal data, but the same broad trends are discernible electronegative ligands such as the halide ions and O-donor ligands give small values, and the much more covalently bonded hydride and carbanionic ligands give the most negative values. The tin data seem to show rather less discrimination between the... 

The hydrides of beryllium and magnesium are both largely covalent, magnesium hydride having a rutile (p. 36) structure, while beryllium hydride forms an electron-deficient chain structure. The bonding in these metal hydrides is not simple and requires an explanation which goes beyond the scope of this book. 

Silicon, unlike carbon, does notiorm a very large number of hydrides. A series of covalently bonded volatile hydrides called silanes analogous to the alkane hydrocarbons is known, with the general formula Si H2 + 2- I uf less than ten members of the series have so far been prepared. Mono- and disilanes are more readily prepared by the reaction of the corresponding silicon chloride with lithium aluminium hydride in ether ... 

Lithium hydride reacts vigorously with siUcates above 180°C. Therefore, glass, quart2, and porcelain containers cannot be used in preparative processes. That only traces dissolve in polar solvents such as ether reflects its significant (60—75%) covalent bond character. It is completely soluble in, and forms eutectic melting compositions with, a number of fused salts. 

In Eq. (6) the hydrogen attached to the oxygen has protonic character and the hydrogen attached to the zinc has hydridic character. Such bonds, with considerable ionic character, would be expected to yield intense bands in the IR, whereas a largely covalent bond would yield relatively weak IR... 

Covalent and polar-covalent bonding 4.4.1 Metal hydrides and alkyls... 

A basic hydride ligand should be present. This is usually realized for electropositive early transition metals or late transition metals in low oxidation states supported by electron-donating ligands. The metals are preferably from the second and third transition series to ensure strong covalent bonding. 

A simple method is given for obtaining root-mean-square electron-cloud radii yr. m. i. from diamagnetism. Comparison of these with structural radii r shows that for ionic and van der Waals bonds, r is about twice yr. m. s.for localised covalent bonds they are about equal. Comparison with theory shows that electron-cloud radii are about the same for localised-bond atoms, or for ions in crystals, as for the free particles with a notable exception in the hydride anion. 

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