Complex Metal-Organic Frameworks from Symmetrically Backfolded Dendrimers

We study symmetrically backfolded building blocks (Sierpinski dendrimers) that generate metal-organic frameworks featuring graphitic ribbons, free-standing carboxylic functions and intricate topologies in clear correspondence with molecular structures. Unlike the starburst shape of traditional dendrimers, the Sierpinski dendrimer features side branches bent away (e.g., by 120º) from the outward direction of the main branch. This paper reports a systematic attempt to correlate the backfolded shape with the connectivity (topology) of the resultant network. Our discovery is surprisingly simple: as building blocks for extended nets, the backfolded Sierpinski dendrimer behaves as a collection of subsidiary building units of the conventional starburst shape (e.g., the regular tritopic unit); and the resultant networks can be deconstructed into subnets corresponding to the star-shaped subunits of the molecule. These seemingly exotic and highly branched molecules are not only compatible with the purpose of network construction, but also present fundamentally new features that open new horizons for molecular design.