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

Abstract

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 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-G 1 N)2 suggest the proposed supramolecular structure. The isosteric heats of CO2 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.

Adsorbing Volatile Organic Chemicals by Soluble Triazine-Based Dendrimers under Ambient Conditions with the Adsorption Capacity of Pyridine up to 946.2 mg/g

“…Dendrons 4 and 5 were prepared according to the literature [ 32 ]. Two equivalents of 4 reacted with 4,4′-bipiperidine in the presence of potassium carbonate in THF to lead the formation of dendrimer 2 in 70% yield.…”

“…In the same manner, the BET surface area of 3 was estimated to be 212.3 m 2 /g. The BET surface areas of dendrimers 2 and 3 were 41 and 56% higher, respectively, than that of 1 (136.0 m 2 /g) [ 32 ].…”

“…On the other hand, dendrimers, generally with significant internal void spaces, are reported to adsorb metal ions or small molecules in solution for the purpose of catalyzing [ 26 , 27 ] and drug delivery [ 28 , 29 , 30 ]. As solids, dendrimers have also been demonstrated to contain dendritic void spaces and adsorb gases [ 31 , 32 ]. However, dendrimers have not yet been used as porous materials to adsorb VOCs.…”

“…However, dendrimers have not yet been used as porous materials to adsorb VOCs. In particular, dendrimers with amide groups at their periphery may have good pyridine adsorbing ability [ 32 ]. Dendrimers constructed by covalent bonding between light atoms, such as carbon, oxygen, and nitrogen, showed low density and high thermal stability comparable to those of ACs and PRs.…”

“…Previously, we prepared dendrimer 1 , with piperazine in the central core and 1,3,5-triamidobenzene (1-3-5-TAB) moiety as a peripheral functionality ( Figure 1 ) [ 32 ], showing the BET value of CO 2 was coming mostly from the distribution of interstitial void space i of the molecules ( Figure 1 ). The peripheral amides were not imbedded in the internal space of each dendritic molecule in the bulk solid, and the void space ii is much less accessible to gases [ 32 ]. In this report, to further increase the void spaces for adsorbing gases or VOCs, we have further designed and prepared dendrimer 2 , with 4,4′-biperidine in the central core and 1-3-5-TAB as the peripheral functionality.…”