Boron-imidazolate Coordination Networks with 3d Transition Metals for Enhanced CO2 Adsorption Capability

The synthesis conditions of a sodalite (SOD)-topology coordination network with a boron-imidazolate framework (BIF), namely BIF-3-Cu, were systematically investigated to control the crystal growth process. By optimising the reaction time, temperature, solvent, reaction reagent, and additives, highly crystalline BIF-3-Cu crystals were obtained, showing high specific surface areas comparable to those of well-known SOD-topology network materials based on zeolitic imidazolate frameworks. Furthermore, we found that the valence of the metal ion plays a vital role in the molecular inclusion into the pores during the crystal nucleation and growth process. Taking advantage of this, new crystals with SOD topology were obtained by a similar reaction using divalent zinc (Zn2+), cobalt (Co2+), and manganese (Mn2+) ions. The resultant crystals contained several monovalent counterions in their pores to compensate for the charge of the cationic framework formed by the divalent metal cations and monovalent anionic boron-bridged ligands. Moreover, the SOD-Zn-BIF exhibits relatively high CO2 adsorption in the narrow micropores, despite the presence of counter anions.