Towards the construction of mesoscopic species with emergent and functional properties via the derivatisation of molybdenum-oxide 'Giant-Wheel' clusters

Polyoxometalate chemistry has proved to be an extraordinary source of a large variety of compounds, clusters and solid-state structures-these are built using very simple metal oxygen fragments linked together in an enormous variety of modes. Herein we focus on the 'Giant-Wheel' clusters which contain 154 and 176 Mo atoms and examine the variety of structural modifications that has been achieved to date with these systems. The generation of structural vacancies (here referred to as defects), substitution of ligands, and incorporation of hetero-metallic centres offers many fascinating possibilities with respect to the targeted functionalisation of these species for a pre-determined function and application. Furthermore, evidence is presented which suggests the identity of the most labile and, therefore, most easily derivatised units present in these systems. The consequences of this assignment are then discussed in the context of inter- (formation of layers and chains) and intra- (assembly inside the cavity) molecular growth. (C) 2000 Elsevier Science B.V. All rights reserved.