Covalent Organic Frameworks

Our main purpose, in the reported research, was the synthesis of three new covalent organic frameworks (COFs) along with their structural characterization. The synthesis procedure, based in the trimerization reaction, allowed the production of the COFs labelled: LH0004, LH006 and LH008. After the synthesis, the obtained materials were thoroughly tested with: IR and Raman spectrometry, X-ray diffraction along with nitrogen adsorption at 77 K.  The interpretation of the IR and Raman study ascertained that the polymerized monomers, i.e., 2, 3-dicyanohydroquinone, 4, 5-dicyanoimidazole and 2, 3-dicyanopyrrzine, were the building blocks of the produced COFs; moreover, the analysis of the XRD profiles, established that their frameworks were consistent with the tetragonal P4mmm space group; in which, the polymeric structure included within the tetragonal unit cell formed 2.3 Å pores; finally, the nitrogen adsorption data demonstrated that the COFs pore size is not enough to let the nitrogen molecule get into their porosity, because the kinetic diameter of the nitrogen molecule, d(N2) = 3.64 Å, while the pore size of the framework is D = 2.3 Å.

This work deals with the investigations of hydrogen adsorption energies of the Li functionalized Covalent Organic Framework-366 (COF-366) by using the density functional theory method. Based on total energy calculations, it was found that Li atom is preferentially trapped at the center site of the tetra (p-amino-phenyl) porphyrin and the onN site of a terephthaldehyde chain. Moreover, hydrogen adsorption energies per H2 for 1e3 H2 loadings range from 0.03 to 0.22 eV. According to ab initio molecular dynamics simulations, our results found that hydrogen capacities of Li functionalized COF-366 at ambient pressure are 2.06, 1.58, and 1.05 wt% for 77, 150 and 298 K, respectively.

A squaraine-linked, conjugated two-dimensional porphyrin covalent organic framework (COF; see scheme; C: gray, H: white, N: blue, Cu: red) was synthesized. Owing to the π-conjugated linkage together with the eclipsed stacking of the units, this COF exhibits enhanced chemical and thermal stabilities. It absorbs a broad range of light, from the ultraviolet to the visible, and near-infrared regions, and shows potential as a photocatalyst.

Covalent organic frameworks (COFs) are an emerging class of crystalline porous polymers in which organic building blocks are covalently and topologically linked to form extended crystalline polygon structures, constituting a new platform for designing π-electronic porous materials. However, COFs are currently synthesised by a few chemical reactions, limiting the access to and exploration of new structures and properties. The development of new reaction systems that avoid such limitations to expand structural diversity is highly desired. Here we report that COFs can be synthesised via a double-stage connection that polymerises various different building blocks into crystalline polygon architectures, leading to the development of a new type of COFs with enhanced structural complexity and diversity. We show that the double-stage approach not only controls the sequence of building blocks but also allows fine engineering of pore size and shape. This strategy is widely applicable to different polymerisation systems to yield hexagonal, tetragonal and rhombus COFs with predesigned pores and π-arrays.

Ordered p-columns and open nanochannels found
in covalent organic frameworks (COFs) could render them
able to store electric energy. However, the synthetic difficulty in
achieving redox-active skeletons has thus far restricted their
potential for energy storage. A general strategy is presented for
converting a conventional COF into an outstanding platform
for energy storage through post-synthetic functionalization
with organic radicals. The radical frameworks with openly
accessible polyradicals immobilized on the pore walls undergo
rapid and reversible redox reactions, leading to capacitive
energy storage with high capacitance, high-rate kinetics, and
robust cycle stability. The results suggest that channel-wall
functional engineering with redox-active species will be a facile
and versatile strategy to explore COFs for energy storage.

In this work, we reveal the coordination of copper ions absorbed by a series of covalent organic frameworks. The frameworks were synthesized through the nucleophilic substitution of either cyanuric chloride or phosphonitrilic chloride trimer by 4,4′-bipyridine, and they were utilized as absorbers for the removal of copper ions from aqueous solutions. The exfoliated counterpart of the layered network was compared to the bulk materials in terms of the copper retention capacity and efficiency. The ion absorption capacity of copper ranged from 100 to 290 mg/g depending on the morphology and chemical structure of the framework. As evidenced by the SEM and XRD analysis, the copper absorption induced certain morphological changes in the networks. EPR spectroscopy revealed the key finding of this study: the trigonal bipyramidal configuration of the copper ions in their divalent state, coordinated with the nitrogen of the core units, 4,4′-bipyridine, and chlorine ions. The analysis of the thoroughgoing experiments bridges the gap between coordination molecular chemistry and the field of covalent organic frameworks. EPR explores how the unique trigonal bipyramidal coordination could be suppressed in the end by the environment and, more specifically, by the addition of glycerol to the aqueous dispersions of the covalent organic frameworks.