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.