We have devised a
straightforward tandem postsynthetic modification
strategy for Zr-based metal–organic framework (MOF) materials,
which resulted in a series of well-defined 2-in-1 heterogeneous catalysts,
cat1
–
cat8
, exhibiting high catalytic activity
in the synthesis of cyclic carbonates under solvent-free and co-catalyst-free
conditions. The materials feature precisely located co-catalyst moieties
decorating the metal nodes throughout the bulk of the MOF and yield
cyclic carbonates with up to 99% efficiency at room temperature. We
use diffuse reflectance infrared Fourier transform (DRIFT) and solid-state
nuclear magnetic resonance (NMR) measurements to elucidate the role
of each component in this model catalytic reaction. Establishing a
method to precisely control the co-catalyst loading allowed us to
observe the cooperativity between Lewis acid sites and the co-catalyst
in the 2-in-1 heterogeneous system.
The efficient capture and storage of radioactive iodine (I or I), which can be formed during nuclear energy generation or nuclear waste storage, is of paramount importance. Herein, we present highly efficient aerogels for reversible iodine capture, namely, porous silsesquioxane-imine frameworks (PSIFs), constructed by condensation of octa(3-aminopropyl)silsesquioxane cage compound and selected multitopic aldehydes. The resulting PSIFs are permanently porous (Brunauer-Emmet-Teller surface areas up to 574 m/g), thermally stable, and present a combination of micro-, meso-, and macropores in their structures. The presence of a large number of imine functional groups in combination with silsesquioxane cores results in extremely high I affinity with uptake capacities up to 485 wt %, which is the highest reported to date. Porous properties can be controlled by the strut length and rigidity of linkers. In addition, PSIF-1a could be recycled at least four times while maintaining 94% I uptake capacity. Kinetic studies of I desorption show two strong binding sites with apparent activation energies of 77.0 and 89.0 kJ/mol. These energies are considerably higher than the enthalpy of sublimation of bulk I.
Homosubstituted amido-functionalized polyoctahedral oligomeric silsesquioxanes (POSS) have been synthesized by using acyl chlorides in high yields (ca. 95%). The method proved to be superior over "conventional" syntheses applying carboxylic acids or acid anhydrides, which are much less efficient (ca. 60% yield). A palette of aryl and alkyl groups has been used as side-chains. The structures of the resulting amide-POSS are supported by multinuclear (1)H, (13)C, (29)Si NMR and FTIR spectroscopy and their full conversion into octasubstituted derivatives was confirmed using mass spectrometry. We also demonstrate that the functionalized silsesquioxanes with bulky organic side-chains attached to cubic siloxane core form spherical-like, well-separated nanoparticles with a size of approximately 5 nm.
In this article, we report on the chemistry and the spectroscopic properties of well-defined imino-functionalized polyoctahedral oligomeric silsesquioxanes (imine-POSS) with various substitutions. Our efforts were mainly focused on side chains with sizable aryl groups possessing hydroxyl, nitro, and halide moieties. Such a choice enabled us to track their reduction abilities to secondary amine-POSS, tautomerization effects, and thermal properties. We also report for the first time the solid-state structures of five imino-functionalized cage-like octasilsesquioxanes. These structures provide unique examples of the complexities of three-dimensional packing motifs and their relationship with the assembly of tunable materials from nanobuilding blocks.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.