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

Abstract

A lanthanide-alkali (HoIII−KI) bimetallic α-Po type 3D framework {KHo(C2O4)2(H2O)4}n (1) (C2O42- = 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 KI 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.