Coordination Polymers and Metal Organic Frameworks
We are particularly interested in the preparation of coordination polymers that may support permanent porosity (metal-organic frameworks, MOFs) as they show promise for applications in catalysis, separation, gas storage and molecular recognition. In contrast to conventional micro-porous inorganic materials such as zeolites, MOFs have the potential for rational design, ranging from the control of the architecture to the functionalisation of the pores. The modularity of an organic ligand (steric-electronic properties, chirality, size and functionalisation etc.) may be fused with the intrinsic physico-chemical properties of transition metals (colour, magnetism, catalysis, chemical and photo-reactivity) to yield 'smart' compounds with manifold potential applications.
Figure 1: The 3D network MOF, {[Mn(dcbp)].2H2O}n, showing H2O molecules within the ca. 0.38 x 0.68 nm channel (left) and their reversible removal to give {[Mn(dcbp)]}n, (right). The vacant channels have the ability to absorb other species. (see Chem. Commun , 2004 , 775; Dalton Trans., 2004 , 3440; CrystEngComm ., 2005 , 7 , 90; CrystEngComm ., 2008 , 10 , 68). H2 dcbp = 4,4'-dicarboxy-2,2'-bipyridine.
We have used poly-pyridine-poly-carboxylate ligands to engage in the organisation of metal ions, Figure 1. We chose these ligands as their progenitor is 2,2'-bipyridine (one of the most widely used ligands in chemistry) which is capable of coordinating to every metal within the periodic table, resulting in the preparation of innumerable coordination complexes with assorted properties. Equally significant within this family are the carboxylate functionalities, which have equal propensity for coordination of metal ions. The marriage of these two coordination functionalities within these ligands, and the successful incorporation of these ligand families into porous MOFs augurs well for the generation of truly unique materials, with hybrid functions, properties and structures. Until our studies, the deliberate use of polypyridine-polycarboxylate ligands in the formation of extended network species had not been attempted. Our current studies build upon the expertise we have gained from our previous endeavours and applies this to the synthesis of new ligand types and their incorporation into framework materials. Both organic synthesis and coordination chemistry lie at the heart of this research.