Soluble dynamic coordination polymers as a paradigm for materials science

Metal ion induced self-assembly of polytopic ligands can be employed to make macromolecular assemblies in solution. This new class of coordination polymers has recently attracted increasing interest. By carefully adjusting the boundary conditions of self-assembly it is possible to form soluble macromolecular assemblies in solution. For this, the binding constants between metal ions and ligands have to be of the appropriate strength. If the interaction is too weak, macromolecular species will not form, but if it is too strong, precipitation may occur. Intermediate binding constants imply a facile exchange of ligands, that is, soluble coordination polymers are generally dynamic equilibrium systems. Through the design of the ligands, the choice of the metal ions and through the pH, ionic strength, temperature and other experimental parameters it is possible to define a window of opportunity where soluble coordination polymers exist. However, the dynamic nature poses a great challenge for characterization because structure and property depend on the external conditions. Besides the value-adding properties of transition metal ions such as electrochemical, magnetic, optical and reactive parameters these polymers add a dynamic component to an already rich spectrum of polymer properties. The dynamic nature makes them unique for fundamental research to address questions concerning self-assembly thermodynamics and kinetics. Additionally, these polymers provide an enormous potential for the development of stimuli-responsive and intelligent materials. (C) 2007 Elsevier B.V. All rights reserved.