Non-aqueous coordination chemistry

   A growing number of complexes (generally air- and moisture- sensitive) involving alkali metal ions with O- or Ndonor ligands and formed in non-aqueous media are now known, although the chemistry of the later group 1 metals is not so widely developed as that of Li. A general method of synthesis is to prepare an alkali metal salt in the presence of a coordinating ligand. For example, in [{LiCl(HMPA)}₄], use of the bulky ligand HMPA (hexamethylphosphoramide), 10.5, results in the isolation of a discrete complex rather than an extended LiCl lattice; the complex contains the cubic Li₄Cl₄ core. Increasing the size of the halogen tends to reduce the nuclearity of the product, e.g. [Li₂Br₂(HMPA)₃]. The bonding in these complexes is of interest can be viewed in terms of a central aggregate of Li‏⁺ and Cl^- ions, and in general, the bonding should be considered to be predominantly ionic.

Amidolithium complexes of type RR’NLi (e.g. R and R’ = alkyl, aryl, silyl) exhibit a fascinating structural diversity; as above, bulky amido ligands are essential for complex stabilization. Planar Li₂N₂-rings are common structural units, and these appear in a variety of laddered structures which may be polymeric or discrete molecular as in [{tBuHNLi}₈] (Figure 1.1).

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