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. 2021 Sep 17;6(38):24637-24649.
doi: 10.1021/acsomega.1c03327. eCollection 2021 Sep 28.

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

Nikolas Király  1 , Vladimír Zeleňák  1 , Nina Lenártová  1 , Adriana Zeleňáková  2 , Erik Čižmár  2 , Miroslav Almáši  1 , Vera Meynen  3 , Andrej Hovan  2 , Róbert Gyepes  4
Affiliations

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

Nikolas Király et al. ACS Omega. .

Abstract

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.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Number of publications from 2003 up to the present (January 2021) found in the Scopus database using the phrase “metal–organic frameworks and porphyrin”.
Scheme 1
Scheme 1. Molecular Structure of 4,4′,4″,4‴-(Porphyrin-5,10,15,20-tetrayl)tetrakis(benzenesulfonic) Acid (H6TPPS) as an Organic Component Used in the Synthesis of UPJS-10 to UPJS-12 Materials
Figure 2
Figure 2
(a) Coordination modes of H2TPPS4– to Pr(III) ions in the crystal structure of {[Pr4(H2TPPS)3]·nH2O}n. (b) View of the -Pr-(SO3)4-Pr- cluster, forming 1D chains propagating along the c crystallographic axis, with the representation of a square planar SBU, (c) square antiprismatic coordination geometry of Pr(III) ions in UPJS-10, and (d) 3D porous framework viewed along the c crystallographic axis.
Figure 3
Figure 3
Experimental kinetics of singlet oxygen phosphorescence produced by excitation of UPJS-10 suspended in water at 630 nm. The experimental curves were fitted by eq 1 (solid black lines).
Figure 4
Figure 4
Thermogravimetric curves of (a) UPJS-10 and (b) UPJS-12.
Figure 5
Figure 5
Argon adsorption/desorption isotherms of UPJS-10 (black curve) and UPJS-12 (red curve) measured at −186 °C.
Figure 6
Figure 6
Carbon dioxide adsorption isotherms of UPJS-10 and UPJS-12 measured at (a) 0 °C and (b) 20 °C.
Figure 7
Figure 7
Temperature dependence of the χT product of UPJS-10, UPJS-12, and [La(H2TPPS)]n·nH5O2+ (open symbols). The solid red line represents the fit of the simplified Van Vleck model using eq 2 for UPJS-12, and the solid blue line represents the fit of the crystal-field Hamiltonian in the Stevens notation for UPJS-10.
Figure 8
Figure 8
Field dependence of the magnetization of UPJS-10, UPJS-12, and [La(H2TPPS)]n·nH5O2+ measured at 1.8 K. The solid red line represents the simulation of the Brillouin function with the effective spin Seff = 1/2 for UPJS-12, and the solid blue line represents the fit of the crystal-field Hamiltonian in the Stevens notation for UPJS-10.
Figure 9
Figure 9
X-band EPR spectra of UPJS-12 measured in the temperature range of 2–20 K. The dotted black line represents the simulation, including one Ce(III) site, while the solid black line includes two Ce(III) sites with slightly different g-tensor anisotropy using an effective spin Seff = 1/2 model within the EasySpin simulation package.
Figure 10
Figure 10
X-band EPR spectra of UPJS-10 measured at 2 K.
Figure 11
Figure 11
X-band EPR spectra of different complexes under study collected in rapid-scan mode at 2 K. Experiment parameters: microwave power, 0.6325 μW; number of points, 2048; number of scans, 2000; repetition rate, 39.16 Hz; modulation amplitude, 1 Oe.
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