Construction of three new Co(ii)-organic frameworks based on diverse metal clusters: highly selective C2H2 and CO2 capture and magnetic properties

Abstract

Using a symmetrical aromatic carboxylic acid ligand, 4,4′-(pyridine-3,5-diyl)bis(3-fluorobenzoic acid) (H₂L), three Co(II)-based metal–organic frameworks, namely, {[Co₃(L)₂(H₂O)₂(HCOO)₂]}_n (1), {[Co₃(L)₃(H₂O)]·4H₂O·2DMF}_n (2) and {[Co₅(L)₄(H₂O)₄(μ₃-H₂O)₂]·11H₂O·6DMF·2(NO₃)}_n (3), have been solvothermally synthesized. Structural analysis demonstrates that 1–3 possess diverse secondary structural units (SBUs). 1 is a 3D network with a binodal (3,6)-connected Schläfli topology based on trinuclear [Co₃(COO)₄(HCOO)₂N₂] SBUs. Compound 2 possesses different trinuclear [Co₃(COO)₆N₃(μ₃-H₂O)] SBUs, which are further extended by L²⁻ to produce a 3D porous network containing 1D channels with a triangular shape along the c axes, and with an uncommon (3,9)-connected topology. In particular, 3 is constructed from unique pentanuclear [Co₅(μ₃-H₂O)₂N₄(COO)₈]²⁺ SBUs to form a (3,12)-connected network, and contains one-dimensional triangular channels. Furthermore, the desolvated frameworks of 2 and 3 show selective adsorption for C₂H₂ and CO₂ over CH₄ at 273 and 298 K. Moreover, the magnetic properties of 1–3 have been completely examined.