Immobilization of Alkali Metal Ions in a 3D Lanthanide-Organic Framework: Selective Sorption and H₂ Storage Characteristics

A lanthanide-alkali (Ho^III−K^I) bimetallic α-Po type 3D framework {KHo(C₂O₄)₂(H₂O)₄}_n (1) (C₂O₄^2- = oxalate dianion) has been synthesized and structurally characterized. Its dehydrated framework 1′, after removal of the K-bound water molecules, is found to exhibit permanent porosity with a clear size selective vapor sorption properties and H₂ storage capability. High heat of H₂ sorption (approximately −10 kJ/mol) observed in experiment is shown to arise from the preferential interaction of H₂ with unsaturated K^I sites decorated on the pore surfaces, using first-principles density functional theory-based calculations of energetics as well as the detailed structure. Our work shows that a material with better hydrogen storage and release properties can be developed through immobilization of unsaturated reactive alkali metal ions at the pore surfaces in a metal-organic framework.