Influence of size and shape on inclusion properties of transition metal-based wheel-and-axle diols

Abstract

It is widely recognized that molecular shape has a key role in orienting and modulating crystal packing efficiency and it is consequently also crucial in determining host-guest properties of solid state materials. This chapter is focused on inclusion propensity of transition metal-based systems designed to have a wheeland-axle shape, which has shown to favour the inclusion of small guest in the solid state. The wheel-and-axle transition metal-based molecules are built by combining a vast library of wheels and axles: the terminal wheels are ligands of different shapes, and the linear axles are made by using metals of different coordination stereochemistry. These systems generally assemble in flexible dynamic frameworks, which can create pores on demand to accommodate small guest molecules. The framework is able to switch between two similarly stable states: the apohost, sustained by host-host contacts, and the solvate form, sustained by host-guest interactions. The transition between the two states is reversible, so that the process can be recycled. In this chapter the role of modifications of size and shape induced by changing metal stereochemistry and wheel hindrance are discussed, showing that both axle linearity and wheel bulkiness are needed to obtain inclusion properties. © Springer Science+Business Media B.V. 2010.