Synthesis and characterization of holmium based metal–organic frameworks

Abstract

Holmium based metal–organic frameworks (MOFs) are attractive due to their potential biomedical and radiotherapeutic applications. Two new three-dimensional MOFs consisting of holmium(III) and 3,3′,5,5′-azobenzenetetracarboxylate (H₄abtc) were prepared. The microporous Ho(III) binuclear MOF (Ho₂-abtc) with the chemical formula of [Ho₂(abtc)_1.5(DMF)₄]·DMF exhibited a three-dimensional framework. A hexacluster (RE₆X₈) based three-dimensional MOF with the chemical formula ([Ho₆(abtc)₃(μ₃-X)₈]·DMA; X = OH⁻/F⁻, DMA = dimethyl ammonium) exhibited Ho₆ clusters bridged by OH⁻/F⁻ ions. The presence of hexaclusters in the holmium MOFs opens up the design of new MOFs for the holmium delivery with high holmium content. The crystal structures of the MOFs were solved. These MOFs are characterized by single-crystal X-ray diffraction (SC-XRD), powder XRD, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), ¹⁹F nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), gas adsorption analysis, and X-ray photoelectron spectroscopy (XPS).