Building units design and scale chemistry

The concept of a building unit (BU) is used in two ways: the first is an a posteriori tool for description of structures which can be used to imagine new topologies originating from the description; the second one, restricted to the routes leading to the solid from the solution, starts from the reality, of these building units in the solution to design new solids obtained by the tuned precipitation of these BUs with proper counterions. The room temperature and the hydrothermal routes are examined. The existence of BUs with different sizes with close topologies, revealed by numerous examples, leads us to define the notion of "scale chemistry'' which concerns the edification of solids with various BUs, either organic, hybrid, or inorganic, and the consequences it has for the corresponding frameworks and the voids they generate. Not only the framework is important, and applications of the existence of large cavities are discussed. The paper ends with a discussion of the new trends which arise from this topological concept. (C) 2000 Academic Press.