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

Abstract

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 Å, 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.