From simple building blocks to structures with increasing size and complexity

In Nature, complex molecular systems like proteins have evolved (natura nat urans) which are perfectly suited to their functions. These are produced in a sequence of steps under dissipative conditions-that is, far from equilib rium. The challenge for the chemist is to nsynthesize correspondingly compl ex multi-functional molecules also under non-equilibrium (non-dissipative) conditions using multi-component, one-pot reactions, without having to sepa rate and purify each single intermediate product. Relevant model reactions have been discovered in solutions of simple oxoanions of the early transiti on metals: novel types of molecular growth processes with feedback (includi ng a type of induced cascade) are described leading to different ring-shape d, electron-rich, mixed-valence, giant polyoxomolybdates with nanosized cav ities. These can-due to the generation of defects-be covalently linked toge ther to form chains as well as layered mesoporous compounds with properties relevant for materials science. They can also start growing again. The lar gest polyoxometalate cluster obtained on the basis of this growth process t o-date has 248 Mo atoms. Remarkably, such giant ring species can also act a s hosts for other clusters forming new types of supramolecular compounds. ( C) 1999 Elsevier Science S.A. All rights reserved.