A Microporous Ni(II) Metal–Organic Framework Nanostructure with an Aspartate-Derived Tricarboxylate for Gas/Vapor Sorption and Size-Selective CO₂ Chemical Fixation under Solvent-Free Conditions

A microporous metal–organic framework {[Ni 4 (μ 3 −OH) 2 ( d -2,4-cbs) 2 (H 2 O) 4 ]·5H 2 O} n ( Ni-CBS ) with a stable Ni 4 (μ 3 –OH) 2 core has been solvothermally synthesized by using an aspartate-derived tricarboxylic acid, H 3 ( d -2,4-cbs). A tapered microrod-like surface morphology of Ni-CBS is observed via field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). Its crystallinity and thermal stability are analyzed using powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA), respectively. The nitrogen adsorption isotherm at 77 K validates the micron-size pores in the framework. The amine-functionalized framework is further utilized to study CO 2 adsorption for a potent interaction between the framework and CO 2 molecules with an isosteric heat of adsorption ( Q st ) value of 33.5 kJ mol –1 at zero loading. Further, the microporous nature of the framework is demonstrated through the encapsulation of various organic solvent molecules. With a high CO 2 uptake value at room temperature (47.8 cm 3 g –1 ), Ni-CBS is found to be a competent heterogeneous catalyst for the formation of cyclic carbonates by fixing carbon dioxide chemically with epoxides of appropriate molecular dimensions. Furthermore, the catalytic behavior of Ni-CBS is compared with the previously reported isostructural Zn-CBS under solvent-free conditions, confirming more Lewis acid character of Zn(II) over Ni(II).