Three novel metal-organic frameworks with different topologies based on 3,3′-dimethoxy-4,4′-biphenyldicarboxylic acid: Syntheses, structures, and properties

A series of three novel metal-organic frameworks, [CdL]_n (1), [ZnL]_n (2), and [Cu₂L₂(DMF)₂] ·6H₂O (3), were successfully prepared by a solvothermal method using 3,3′-dimethoxy-4,4′-biphenyldicarboxylic acid (H ₂L) as the ligands. X-ray crystallography analysis reveals that complex 1 exhibits a 3D framework with sra topology and a rare eight-coordinated Cd(II) with two bound methoxy groups as secondary building unit (SBU). For complex 2, a 2D coordination network with a four-coordinated Zn(II) as SBU was observed. Complex 3 also shows a 2D layered architecture with 44 square lattice topology and a paddle-wheel Cu₂(-CO₂)₄ as SBU. ¹¹³Cd NMR spectrum of 1 showed that the chemical shift of eight-coordinated Cd(II) appeared at δ - 108.9 ppm. In addition, both 1 and 2 are robust coordination polymers with high thermal stabilities (> 380 °C). Fluorescence measurements of 1 and 2 display medium strong emission peaks at 403 and 401 nm, respectively. Magnetic study of 3 exhibits a strong antiferromagnetic interaction between two Cu(II) ions with -2J = 286 cm ^-1.