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(C 2 O 4 ) 2 (H 2 O) 4 } n ( 1 ) (C 2 O 4 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 H 2 storage capability. High heat of H 2 sorption (approximately −10 kJ/mol) observed in experiment is shown to arise from the preferential interaction of H 2 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.