Coordination polymer open frameworks constructed of macrocyclic complexes

Abstract

Coordination polymer open frameworks having voids and channels of various aperture sizes and shapes can be assembled by using metal azamacrocyclic complexes and organic carboxylates as molecular building blocks. In the assembly, the azamacrocyclic complexes in square-planar geometries act as linear linkers for the carboxylate ligands that have linear, triangular, and tetrahedral shapes to provide primary 1D, 2D, and 3D networks. The primary networks pack three-dimensionally in the solid state to generate open structures with pores and channels. Some of the coordination polymer open frameworks show porosity and hydrogen storage capabilities (up to 1.0 wt% at 77 K and 1 atm). The hydrogen storage data are better than those for zeolites but not as good as those of the metal-organic frameworks prepared from free metal ions. The coordination polymer open frameworks generate various degrees of hydrophobic or hydrophilic environments on the surface of the voids, which are advantageous for the selective binding of organic guest molecules. In addition, some coordination polymers containing flexible molecular components show sponge like shrinkage on removal of the guest molecules that involves dynamic motions of molecular components. In particular, the coordination polymer frameworks incorporating Ni(II) macrocyclic species are redox-active in the solid state and react with the solutions of oxidizing agents such as I2 and Ag+ to produce oxidized frameworks incorporating Ni(III) species and the reduced substrate such as I3 - anions and the small-sized silver nanoparticles. A variety of azamacrocyclic complexes that contain various functional groups attached to the macrocycles can be prepared by the simple template condensation reactions. By employing them as the metal building blocks, various types of networks are expected to be prepared, which would show high specificity for particular guests, novel crystal dynamics, and the formation of nanoparticles from various metal ions.