Edge-directed assembly of a 3D 2p–3d heterometallic metal–organic framework based on a cubic Co₈(TzDC)₁₂ cage

A three-dimensional (3D) heterometallic metal–organic framework containing cubic-like cages, namely {[Co₃Na₆(TzDC)₄(H₂O)₆]·7H₂O}_n (1) (H₃TzDC = 1,2,3-triazole-4,5-dicarboxylate), has been synthesized by the edge-directed self-assembly of TzDC³⁻, Co²⁺ and Na⁺ ions. Crystal data reveals that one hydrous Co²⁺ cation is embedded in the central cavity of a cubic-like cage [Co₈(TzDC)₁₂]²⁰⁻ with eight Co²⁺ cations as the corners and twelve TzDC³⁻ ligands as the edges. The cages are further bridged by Na⁺ ions to result in a 3D framework with pcu topology. Magnetic investigation indicates that besides the spin–orbit coupling of Co²⁺ ions, an antiferromagnetic exchange interaction was found to exist between the Co²⁺ ions in the Co₉ cluster of 1.