American Chemical Society
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Novel Lanthanide(III) Porphyrin-Based Metal–Organic Frameworks: Structure, Gas Adsorption, and Magnetic Properties

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journal contribution
posted on 2021-09-17, 23:43 authored by Nikolas Király, Vladimír Zeleňák, Nina Lenártová, Adriana Zeleňáková, Erik Čižmár, Miroslav Almáši, Vera Meynen, Andrej Hovan, Róbert Gyepes
The present work focuses on the hydrothermal synthesis and properties of porous coordination polymers of metal–porphyrin framework (MPF) type, namely, {[Pr4(H2TPPS)3]·11H2O}n (UPJS-10), {[Eu/Sm­(H2TPPS)]·H3O+·16H2O}n (UPJS-11), and {[Ce4(H2TPPS)3]·11H2O}n (UPJS-12) (H2TPPS = 4,4′,4″,4‴-(porphyrin-5,10,15,20-tetrayl)­tetrakisbenzenesulfonate­(4-)). The compounds were characterized using several analytical techniques: infrared spectroscopy, thermogravimetric measurements, elemental analysis, gas adsorption measurements, and single-crystal structure analysis (SXRD). The results of SXRD revealed a three-dimensional open porous framework containing crossing cavities propagating along all crystallographic axes. Coordination of H2TPPS4– ligands with Ln­(III) ions leads to the formation of 1D polymeric chains propagating along the c crystallographic axis. Argon sorption measurements at −186 °C show that the activated MPFs have apparent BET surface areas of 260 m2 g–1 (UPJS-10) and 230 m2 g–1 (UPJS-12). Carbon dioxide adsorption isotherms at 0 °C show adsorption capacities up to 1 bar of 9.8 wt % for UPJS-10 and 8.6 wt % for UPJS-12. At a temperature of 20 °C, the respective CO2 adsorption capacities decreased to 6.95 and 5.99 wt %, respectively. The magnetic properties of UPJS-10 are characterized by the presence of a close-lying nonmagnetic ground singlet and excited doublet states in the electronic spectrum of Pr­(III) ions. A much larger energy difference was suggested between the two lowest Kramers doublets of Ce­(III) ions in UPJS-12. Finally, the analysis of X-band EPR spectra revealed the presence of radical spins, which were tentatively assigned to be originating from the porphyrin ligands.