Alkaline cation directed structural diversity of cubic-cage-based cobalt(II) metal–organic frameworks: from pcu to bct net

Three 2p–3d heterometallic cubic-cage-based metal–organic frameworks (MOFs), formulated as {[H2N(CH3)2]9(H3O)6[Co(H2O)6][Co8Li3(TDA)12]·14H2O}n (1), {(H3O)15[Co(H2O)6][Co8Li3(TDA)12]·10H2O}n (2) and {[H2N(CH3)2](H3O)16[Co8K5(μ2-O)(TDA)12(H2O)2]·10H2O}n (3) (H3TDA = 1H-1,2,3-triazole-4,5-dicarboxylic acid), have been successfully synthesized and structurally characterized in detail. In these 2p–3d heterometallic cubic-cage-based MOFs, eight Co2+ cations as the vertexes are interconnected by twelve TDA3− ligands as the edges to form an unusual [Co8(TDA)12]20− cubic cage with edges of 6.12 A, in which a hexahydrated Co2+ ion is captured for 1 and 2. The neighboring [Co8(TDA)12]20− cubic cages are further bridged by Li+ ions for 1 and 2 and K+ ions for 3 to give 3D 6-connected pcu nets for 1 and 2 and a 10-connected bct net for 3. The magnetic properties of 1–3 were studied in detail.