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

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, {[Co-3(L)(2)(H2O)(2)(HCOO)(2)]}(n) (1), {[Co-3(L)(3)(H2O)]center dot 4H(2)O center dot 2DMF}(n) (2) and {[Co-5(L)(4)(H2O)(4)(mu(3)-H2O)(2)]center dot 11H(2)O center dot 6DMF center dot 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 Schlafli topology based on trinuclear [Co-3(COO)(4)(HCOO)(2)N-2] SBUs. Compound 2 possesses different trinuclear [Co-3(COO)(6)N-3(mu(3)-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 [Co-5(mu(3)-H2O)(2)N-4(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.