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Magneto-Structural Correlations in Ni(II)-MOF-74 and Intermediate Compounds Studied by HF-ESR Spectroscopy

Metal–organic frameworks (MOFs) have attracted huge interest due to their promising properties for applications as gas-storage systems, sensors, and catalysts [1] but also because of their magnetic properties.[2] They could be defined as a class of porous polymeric materials, consisting of metal ions bridged by organic ligands. One of intensively investigated and commercially available MOF materials is MOF-74, characterized by honeycomb structure with short distances among the metal centers and open metal sites. Here we present electron spin resonance (ESR) study of magnetic properties of Ni(II)-MOF-74 (Ni-MOF) and of a non-porous intermediate complex (Ni-INT) detected and isolated during the synthesis of Ni-MOF material (Fig. 1). Also, we investigated the properties of Ni-MOF when the coordination sphere of the metal sites was changed by removing the labile coordinated ligands (Ni-MOF-empty)[3] and the properties of the amorphous Ni-MOF with collapsed MOF architecture and non-existent long-range ordering (Ni-MOF-amorph). Using the results obtained from multi-frequency (up to 321 GHz) high-field (up to 16 T) ESR (HF-ESR) as well as X-band ESR and magnetization measurements together with X-ray diffraction data, the magneto-structural correlation of the compounds will be discussed. [1] T. Yamada et al. Chem. Soc. Rev. 2013 42 6569 [2] P. Canepa et al. Phys. Rev. B 2013 87 094407 [3] A. M. Sheveleva et al. J. Phys. Chem. C 2017 121 19880 This work has been supported by Croatian Science Foundation under the projects HrZZ-UIP-2014-09-4744 and HrZZ 1108.

MOF ; Ni(II) ; ESR/EPR ; high-field

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