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

Cheng-Hua Lee,Kuang-Lieh Lu,Long-Li Lai,Chung-Hao Tzeng,Dmitriy V Soldatov

doi:10.1038/s41598-017-03684-y

Abstract

Three dendrimers, (t-Bu-G2N)2, CC(t-Bu-G1N)3 and (t-Bu-G1N)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 m2/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-G1N)2 suggest the proposed supramolecular structure. The isosteric heats of CO2 sorption (Qst) for (t-Bu-G2N)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.

Highlights

The case of POFs and COFs, their void space at the atomic level can be understood and the porosity of the overall material can be designed, as demonstrated previously for MOFs and HOFs
This study shows that triazine-based dendrimers have a potential application in separating N2 from CO2 in a N2 - CO2 mixture
We have prepared a series of dendrimers containing piperazine and triazine as connecting units and 3,5-di-tert-butylamidobenzene as a peripheral moiety

Summary

Introduction

The case of POFs and COFs, their void space at the atomic level can be understood and the porosity of the overall material can be designed, as demonstrated previously for MOFs and HOFs. All three were observed to possess similar BET surface areas in spite of different molecular weights (from 1791 to 2890), which indicates that peripheral amide moieties do not embed in the interstitial space of the dendritic molecules upon their stacking in a bulk solid material. The void space in the dendritic framework can be tuned by changing the connecting fragments of the dendrimers In contrast to their similar sorption capacities, the isosteric heats for CO2 sorption (Qst) of (t-Bu-G2N)[2] are higher than those for the two others, indicating a stronger interaction and prospects for the design of materials with catalytic activity.

Methods

Results

Conclusion