Diamondoid Three-Dimensional Metal-Organic Framework Showing Structural Transformation with Guest Molecules

Abstract

The potential of carboxylate and imidazole-based mixed ligands for forming metal organic frameworks (MOFs) is demonstrated with 4-(1H-imidazole-1-yl)benzoic acid (HIBA) to generate a flexible material. Reaction of HIBA with Cd(NO3)2·6H2O under solvothermal condition in N,N-dimethylformamide (DMF), produces a three-dimensional MOF, {[Cd(IBA)2].2DMF}n (1⊃2DMF), which on heating at 60 and 200 °C turns opaque, forming {[Cd(IBA)2]·DMF}n (1⊃DMF) and {[Cd(IBA)2]}n (1), respectively, as characterized by PXRD, TGA, and elemental analysis. Either of these compounds on keeping in dry DMF for 15 days affords the original compound, i.e., showing reversibility deduced from PXRD. When a crystal of 1⊃2DMF is immersed in moist N,N-diethylformamide (DEF) in a vial open to atmosphere, a new compound, {[Cd(IBA)2]·DEF·H2O}n, (2) is formed in 1 month in a single-crystal to single-crystal (SC-SC) fashion. Also, a crystal of 1⊃2DMF on immersing in moist DMF produces another interesting 3D framework {[Cd(IBA)2.H2O]·DMF·3H2O}n, (3) in a SC-SC transformation. These coordination polymers show interesting 4-fold interpenetrating diamondoid 3D network structures.