Structure and Bonding in Metal Alkyls

Metal alkyls also form aggregates, and the association of LiC2H5 has been investigated by the technique of mass spectrometry. The ions found in the mass spectrum consist of Li R + with n= 1 to 6. However, the appearance potentials (which are associated with the ease of producing these ions) are considerably lower than for ions having other composition. Therefore, it was concluded that the equilibrium in the vapor is predominantly 

The four lithium atoms reside at the comers of the tetrahedron, and a methyl group is located above the center of each triangular face. In the solid phase, the structure is body-centered cubic with a (LiCH3)4 unit at each lattice site. Solid LiC4H9 also consists of tetramers, and these units persist in solutions. 

The structure of the methyl lithium tetramer. Only two methyl groups have been 

Measurements of the molecular weights of aluminum alkyls in benzene solutions indicate that the methyl, ethyl, and n-propyl compounds exist as dimers. However, the heat of dissociation of the (A1R3)2 dimers varies with the alkyl group as shown by the following values  

As described in Chapter 3, the solubility parameter, 8, can often be used as a diagnostic tool for studying molecular association. Table 21.1 shows some of the relevant data for several 

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