Type 7 complexes, which form when s-LUMO Lewis acids complex with Lobe-HOMO Lewis bases, are commonly used as the basic reagents of organic and inorganic chemistry: methyl lithium, sodamide, potassium hydroxide, sodium fluoride, potassium hydrogen phthalate, etc. Type 7 complexes are generally ionic or highly polar covalent species (ie they are charge controlled complexes) and are soluble in polar solvents. The proton abstracting power of a particular Type 7 reagent depends upon the pKa of its conjugate Brønsted acid as proton abstraction power is only subtly altered by the s-LUMO Lewis acid counter ion. Lithium Type 7 complexes are less ionic and less basic than the corresponding sodium salts. Li+ < Na+ < K+ < Cs+ For more information look in the Chemogenesis
webbook sections on Lewis
acids and Lewis bases and the Lewis
acid/base interaction matrix.