Design of a Peripheral Building Block for H-Bonded Dendritic Frameworks and Analysis of the Void Space in the Bulk Dendrimers

Three dendrimers, (t-Bu-G (2) N)(2), CC(t-Bu-G (1) N)(3) and (t-Bu-G (1) N)(2), with 3,5-di-tert-butyl amidobenzene as a common peripheral moiety were prepared in 64–83% yields and characterized. The bulk solids had high BET surface areas of 136–138 m(2)/g, which were similar for the three dendrimers in spite of their different molecular weight (ranging from 1791 to 2890). It was concluded that the peripheral amide groups do not imbed in the interstitial space of neighbouring dendrimer molecules but rather build a supramolecular architecture through strong intermolecular H-bonds. This mode of assembly generates voids in the bulk dendrimers responsible for sorption properties. The X-ray crystal structure analysis of a compound representing the peripheral moiety of the dendrimers and the FT-IR and powder-XRD data for (t-Bu-G (1) N)(2) suggest the proposed supramolecular structure. The isosteric heats of CO(2) sorption (Q (st)) for (t-Bu-G (2) N)(2) were significantly higher than those for the other two dendrimers, which is consistent with the formation of a different type of voids within the interstitial space of the molecule. It is suggested that the interstitial void space can be designed and tuned to adjust its properties to a particular task, such as the separation of gases or a catalytic reaction facilitated by the dendrimer.