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

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 (6-8) stabilized by one-dimensional {Ln(COO)₅Na₂(H₂O)₂(μ₂-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.