UC Berkeley

Chapter 1. Introduction to the fundamentals of reticular chemistry, metal–organic frameworks and covalent organic frameworks.

Chapter 2. Covalent organic frameworks (COFs) are almost entirely based on reversible condensation reactions. This precludes their stability in the presence of water, especially under strongly acidic and basic conditions; simply put, they are prone to hydrolysis. Strategies such as linkage conversion and stabilizing the linkage through covalent functionalization of building units have been developed to overcome these shortcomings, but they require elaborate synthetic efforts to obtain the desired stability. Here, we report a synthetic strategy based on an irreversible nucleophilic aromatic substitution reaction (SNAr) for the synthesis of COFs. In this chapter, we report the synthesis of two new crystalline, porous COFs, termed COF-316 and 318, constructed from new dioxin linkages (C–O bond). For the first time, SNAr reaction has been translated into COF linkage chemistry. The resultant COFs have high chemical stability under both acidic and basic conditions. The utility of this approach is highlighted by two new post-synthetic modification reactions carried out on the COF-316 backbone necessitating extreme conditions, yielding two new functionalities, amide and amidoxime in COFs, which were inaccessible previously.

Chapter 3. Covalent organic frameworks (COFs) can be categorized into 2D and 3D topologies based on the number of vertices, edges, rings and tiles. While the majority of the COFs reported to date are 2D layered structures, there are only five possible 2D topologies with one kind of edge, and all the 2D COFs belong to these five or defected versions. Strategies such as mixing more than two kinds of linkers and desymmetrizing the linkers by changing the edge lengths or vertex angles have been developed to increase the structural diversity of COFs, but fundamentally the underlying topologies still remain limited to the five aforementioned structural types. In this chapter, we report a synthetic strategy for the synthesis of COFs with new topologies that have more than one kind of edge. Specifically, a new crystalline, porous COF, termed COF-346, based on imine linkage with a new tth topology was synthesized (topologies are denoted by unique lowercase bolded three-letter identifiers, same as below). For the first time, linkers with three different connectivity (3, 4 and 6-connected) have been incorporated into one COF by precisely chosen geometry and metrics of linkers. We also report two additional structurally related COFs termed COF-360, with a rare kgd (kagome dual lattice) topology, and COF-340, with a defected tth topology. This work serves to expand the scope of 2D COF structures and realize new strategies for increasing complexity of COFs by design.

Chapter 4. Fundamentally, it is known to be a challenge to use single elongated organic component for the construction of MOFs with ultrahigh porosity due to the limited solubility of large linkers and the propensity of framework interpenetrations. In addition, activation of such materials is rather difficult as the large pores are especially susceptible to collapse. In this chapter we report the synthesis, crystal structure, and porosity of four Zn4O(-COO)6-based MOFs with the nia-net (the same topology as NiAs) using triptycene-derived hexatopic linkers, termed MOF-2008, Zn4O(Trip-Ph), Trip-Ph = 2,3,6,7,14,15-hexakis(4-benzoate) triptycene, MOF-2011, Zn4O(TripMe-Ph), TripMe-Ph = 2,3,6,7,14,15-hexakis(4-benzoate)-9,10-dimethyl triptycene, MOF-2015, Zn4O(Trip-Naph), Trip-Naph = 2,3,6,7,14,15-hexakis(4-naphthoate) triptycene, and MOF-2020, Zn4O(Trip-Biph), Trip-Biph = 2,3,6,7,14,15-hexakis(4’-biphenylcarboxylate) triptycene. MOF-2020 retained ultrahigh porosity upon successful activation, demonstrating its structural integrity, and showed the highest BET surface area (6160 m2 g-1) and pore volume (3.05 cm3 g-1) among the series.

Chapter 5. Ultrahigh-capacity methane storage is essential for heavy-duty vehicles fueled by methane. However, it s still rare for MOFs to achieve the Department of Energy (DOE) target for methane storage systems at 35 or 65 bar. In this chapter, we report the high pressure methane adsorption results based on the four NiAs-typed MOFs developed in the previous chapter. MOF-2008 and -2020 exhibited exceptional volumetric and gravimetric methane working capacities, respectively. MOF-2008 has a volumetric working capacity of 271 cm3 cm-3 (from 5.8 to 200 bar at 298 K), representing a remarkable 27% improvement compared to the compressed natural gas (CNG). MOF-2020 has a gravimetric working capacity of 0.666 g g-1, which is the highest among MOFs, to our certain knowledge, surpassing the current DOE target (0.5 g g-1) by 33%.

Chapter 6. Conclusion and outlook in reticular chemistry.