Complex Formation in Hyperalkaline Solutions

Abstract

Strongly alkaline conditions in aqueous systems may give rise to the formation of novel, so far undiscovered metal complexes, and crystallization from these systems often yields solid materials with peculiar local structures. This is of particular importance from a practical point of view, since the knowledge of the structure and dynamics of these solution species could be the key to understand and to manipulate a large variety of processes, both industrial and geochemical. The current contribution is focused on solution species with ligands as hydroxides, organic molecules with O-donor atoms, or both, which do not form or are undetectable at moderate pH. The possible formation of polynuclear complexes as well as various dehydration products is also discussed. A further important aspect is the characterization of the solids obtained from these systems in terms of both the local symmetry of the complexing ion, i.e. interrelations between solution and the solid structure or the lack of them, and their morphology and/or composition. The general theme of this chapter is that hyperalkalinity, an extreme condition, and unusual chemical events are expected to occur under such conditions.