Largely Entangled Diamondoid Framework with High-Density Urea and Divergent Metal Nodes for Selective Scavenging of CO2 and Molecular Dimension-Mediated Size-Exclusive H-Bond Donor Catalysis

Pore environment modulation with high-density polarizing groups in metal-organic frameworks (MOFs) can effectively accomplish selective and multicyclic carbon dioxide (CO₂) adsorption, whereas the incorporation of task-specific organic sites inside these porous vessels promise to evade self-quenching, solubility, and recyclability issues in hydrogen-bond donating (HBD) catalysis. However, concurrent amalgamation of both these attributes over a single platform is rare but extremely demanding in view of sustainable applications. We designed a robust diamondoid framework CSMCRI-17 (CSMCRI = Central Salt and Marine Chemicals Research Institute) from the mixed-ligand assembly of azo group-containing dicarboxylate ligand, urea-functionalized pyridyl linker, and Zn(II) nodes with specific divergent coordination. Seven-fold interpenetration to the microporous structure largely augments N-rich functionality that facilitates high CO₂ uptake in the activated form (17a) with good CO₂ selectivity over N₂ and CH₄ that outperform many reported materials. The framework displays very strong CO₂ affinity and no reduction in adsorption capacity over multiple uptake-release cycles. Benefitting from the pore-wall decoration with urea functionality from the pillaring strut, 17a further demonstrates hydrogen-bond-mediated Friedel-Crafts alkylation of indole with β-nitrostyrene under mild conditions, with multicyclic usability and excellent reactivity toward wide ranges of substituted nucleophiles and electrophiles. Interestingly, interpenetration-generated optimum-sized pores induce poor conversion to sterically encumbered substrate via molecular dimension-mediated size selectivity that is alternatively ascribed from additional control experiments and support the occurrence of HBD reaction within the MOF cavity. The catalytic path is detailed in light of the change of emission intensity of the framework by the electrophile as well as the judicious choice of the substrate, which authenticates the prime role of urea moiety-governed two-point hydrogen bonding.

Hetero-interpenetrating porous coordination polymers

Interpenetrating porous coordination polymers (IPCPs) consist of two or more networks that are mechanically interlocked to form a coherent structure. The framework topology and the chemical composition are the two important criteria of interpenetrating networks to distinguish homo-IPCPs from hetero-IPCPs. Compared to rich homo-IPCPs, hetero-IPCPs remain rare and are formed rather unexpectedly. This Frontier article highlights hetero-IPCPs in accordance with the difference and/or identity of individual networks in terms of the framework topology and the chemical composition.

On the group-theoretical approach to the study of interpenetrating nets

Using group–subgroup and group–supergroup relations, a general theoretical framework is developed to describe and derive interpenetrating 3-periodic nets. The generation of interpenetration patterns is readily accomplished by replicating a single net with a supergroupGof its space groupHunder the condition that site symmetries of vertices and edges are the same in bothHandG. It is shown that interpenetrating nets cannot be mapped onto each other by mirror reflections because otherwise edge crossings would necessarily occur in the embedding. For the same reason any other rotation or roto-inversion axes fromG \ Hare not allowed to intersect vertices or edges of the nets. This property significantly narrows the set of supergroups to be included in the derivation of interpenetrating nets. A procedure is described based on the automorphism group of aHopf ring net[Alexandrovet al.(2012).Acta Cryst.A68, 484–493] to determine maximal symmetries compatible with interpenetration patterns. The proposed approach is illustrated by examples of twofold interpenetratedutp,diaandpcunets, as well as multiple copies of enantiomorphic quartz (qtz) networks. Some applications to polycatenated 2-periodic layers are also discussed.

An acentric 3-D metal–organic framework with threefold interpenetrated diamondoid network: second-harmonic-generation response, potential ferroelectric property and photoluminescence

An solvothermally synthesized acentric 3-D Cd(ii) metal–organic framework was found to exhibit a unique threefold-interpenetration diamondoid architecture, second-harmonic-generation efficiency, potential ferroelectric property and photoluminescence.