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Continuous-wave EPR study of MOF-525 and PCN-223 doped with various paramagnetic centers

Metal-organic frameworks (MOFs) are porous coordination polymers built from metal nodes and organic linkers [1]. These materials have a potential to be used in spintronics as molecular spin qubits [2]. The magnetic properties of two multivariate porphyrinic Zr-MOFs: MOF-525 and PCN- 223 [2], with 10% copper(II) or vanadyl(IV) cations in porphyrin linker, were examined by continuous-wave electron paramagnetic resonance (CW-EPR) spectroscopy. The simulations of the experimental data, obtained using EasySpin software [3] show that the CW-EPR spectra of MOF- 525 and PCN-223 with copper(II) cations exhibit superhyperfine interaction with four neighboring nitrogen nuclear spins (IN = 1). In contrast, such interactions are not visible for MOF-525 and PCN-223 with vanadyl(IV) cations. This can be explained by the fact that the unpaired electron in the vanadyl(IV) cation resides in the dxy orbital which is well separated from the orbitals of the nitrogen atoms [4, 5]. [1] H. Li, M. Eddaoudi, T. L. Groy, O. M. Yaghi, J. Am. Chem. Soc. 120 (1998) 8571-8572. [2] B. Karadeniz, D. Žilić, I. Huskić, L. S. Germann, A. M. Fidelli, S. Muratović, I. Lončarić, M. Etter, R. E. Dinnebier, D. Barišić, N. Cindro, T. Islamoglu, O. K. Farha, T. Friščić, K. Užarević, J. Am. Chem. Soc. 141 (2019) 19214−19220. [3] S. Stoll, A. Schweiger, J. Magn. Reson. 178 (2006) 42-55. [4] P.Basu, J. Chem. Educ. 78 (2001) 666- 669. [5] M. Atzori, L. Tesi, E. Morra, M. Chiesa, L. Sorace, R. Sessoli, J. Am. Chem. Soc. 138 (2016) 2154−2157.

metal organic frameworks ; copper ; vanadium ; continuous-wave EPR spectroscopy

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