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Open MOFs with Unique Hexatopic Zinc-5,15-bis(4′-carboxyphenyl)-10,20-bis(3′,5′-dicarboxyphenyl)porphyrin Linker

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journal contribution
posted on 28.11.2017, 00:00 by Bharat Kumar Tripuramallu, Soumyabrata Goswami, Israel Goldberg
Characteristic coordination modes of tetrapodal and octapodal porphyrin linkers were combined in the design of a new hexapodal porphyrin linker. The custom-designed [(5,15-bis­(4′-carboxyphenyl)-10,20-bis­(3′,5′-dicarboxyphenyl)]­porphyrin (H6HCPP) contains two trans-related 4-carboxyphenyl coordination sites similar to tetra­(carboxyphenyl)­porphyrin (H4TCPP) linker and two other 3,5-dicarboxyphenyl (isopthalate-type) functions related to octa­(carboxyphenyl)­porphyrin (H8OCPP) moiety. Synthesis of the H6HCPP was optimized for higher yields by utilizing excess concentration of TFA. The supramolecular reactions of zinc metalated linker Zn-H6HCPP with different metal centers afforded open hexacarboxy–metalloporphyrin frameworks (hcMPFs) perforated by wide intralattice voids. One 6-connected uninodal and two 6,6-connected binodal frameworks Mn-hcMPF (1), Co-hcMPF (2), and Zn-hcMPF (3) were obtained by employing transition metals Mn­(II), Co­(II), and Zn­(II) as the exocyclic interporphyrin binding nodes. These frameworks feature dinuclear Mn2 and Zn2 paddlewheels in 1 and 3, and trinuclear Co3 trigonal prisms in 2, as inorganic building units. Among p-block elements In­(III) from the 13th group and Pb­(II) from the 14th group of the periodic table form In-hcMPF (4) and Pb-hcMPF (5) frameworks tessellated by InNa2 and Pb2 clusters as building units. Similar reactions with rare earth elements yielded the formation of Ln-hcMPFs (Ln = Pr­(III), Gd­(III), and Yb­(III)) structures (68) stabilized by one-dimensional {Ln­(COO)5Na2(H2O)22-H2O)2}n heterometallic helical chains with tetragonal shaped interporphyrin channel voids in 6 and 7 and homometallic dinuclear Yb2 cluster in 8. All the frameworks are noninterpenetrated and provide wide solvent accessible intralattice voids, which account for about 53–64% of the crystal volume. Thermal and powder diffraction analyses provided additional insights into the homogeneity and stability of these frameworks.