A new method of synthesis was developed for the flexible coordination polymer Ni(L)[Ni(CN)4], L=1,2-bis(4-pyridyl)ethylene (bpene) to increase its CO2 sorption uptake. The structure of the newly synthesized bpene has been determined by synchrotron X-ray single crystal diffraction. The material was found to be monoclinic, space group P21/m (No. 11), a = 13.5941(12) Å, b = 14.3622(12) Å, c = 12.2562(12) Å, β=96.14(1)º, V = 2767.4(4) Å3, Z= 4, Dc= 1.457 g cm-1. Ni(bpene)[Ni(CN)4] assumes a pillared layer structure with layers defined by Ni[Ni(CN)4]n nets and bpene ligands acting as pillars. Disordered free bpene ligands and solvents of crystallization including dimethylsulfoxide (DMSO) and water molecules occupy the pores, resulting in a formula of Ni2N7C24H25SO3. Without the inclusion of free bpene ligands and solvent molecules, the free volume that could contain adsorbate molecules is approximately 61% of the total volume; this free volume fraction is reduced to 50% with the free ligands present. Pores without the free ligands were found to have a local diameter of 5.7 Å and a main aperture of 3.5 Å. The improved synthetic technique yielded a polycrystalline material with 40% higher CO2 uptake compared to the previously reported powder material. The CO2 adsorption isotherm at 0°C shows an adsorption capacity of 400 mg/g at 8 bar, with a threshold pressure for adsorption of approximately 4 bar. Desorption of CO2 occurs in two distinct steps with significant adsorption-desorption hysteresis.
Citation: Crystal Growth & Design
Pub Type: Journals
Flexible MOF, Flexible Pillared Layer Porous Coordination Polymer, Ni(1, 2-bis(4-pyridyl)ethylene)[Ni(CN)4], single crystal structure, Improved powder synthesis technique, CO2 adsorption/desorption