Bimodal magneto-luminescent dysprosium (DyIII)-potassium (KI)-oxalate framework: magnetic switchability with high anisotropic barrier and solvent sensing

We report synthesis, characterization, and properties of a multifunctional oxalate framework, {KDy(C₂O₄)₂(H₂O)₄}<i>_n</i> (<b>1</b>) (C₂O₄^2- = oxalate dianion) composed of two absolutely different metal ions in terms of their size, charge, and electronic configuration. Dehydrated framework (<b>1′</b>) exhibits permanent porosity and interesting solvent (H₂O, MeOH, CH₃CN, and EtOH) vapor sorption characteristics based on specific interactions with unsaturated alkali metal sites on the pore surface. Compound <b>1</b> shows solvent responsive bimodal magnetic and luminescence properties related to the DyIII center. Compound <b>1</b> exhibits reversible ferromagnetic to antiferromagnetric phase transition upon dehydration and rehydration, hitherto unknown for any lanthanide based coordination polymer or metal-organic frameworks. Both the compounds <b>1</b> and <b>1′</b> exhibit slow magnetic relaxation with very high anisotropic barrier (417 ± 9 K for <b>1</b> and 418 ± 7 K for <b>1′</b>) which has been ascribed to the single ion magnetic anisotropy of the Dy^III centers. Nevertheless, compound <b>1</b> shows a metal based luminescence property in the visible region and H₂O molecules exhibit the strongest quenching effect compared to other solvents MeOH, MeCN, and EtOH, evoking <b>1′</b> as a potential H₂O sensor.