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(mu(3)-OH)(2)(d-2,4-cbs)(2)(H2O)(4)]<middle dot>5H(2)O}(n) (Ni-CBS) with a stable Ni-4(mu(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 CO2 adsorption for a potent interaction between the framework and CO2 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 CO2 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).