The effect of reaction conditions on the nature of cadmium 1,3,5-benzenetricarboxylate metal-organic frameworks

The product from the reaction between Cd(NO₃)₂·4H₂O and 1,3,5-benzenetricarboxylic acid (H₃btc) in DMF at 95 °C depends on the reaction time, with [Cd(Hbtc)(H₂O)₂] 1 and [Cd(Hbtc)(DMF)₂] 2 isolated after heating for 10 min, the latter after standing the solution for 1-2 weeks at room temperature. [Cd₃(btc)₂(H₂O)₉]·4H₂O 3 was isolated after heating for 1 h, whereas [Cd₁₂(btc)₈(DMF)₁₄(OH₂)₂]·1.5DMF 4 was isolated after heating for 2 days. Compounds 1 and 3 have been previously reported, whereas 2 and 4 are both new. Compound 2 adopts a two-dimensional sheet structure, with the coordinated DMF ligands projecting from both sides of the sheets, whereas 4 has a complex three-dimensional structure related to the fsc net. When the reaction was repeated in the presence of pyrazine (pyz), the product [Cd(Hbtc)(pyz)(DMF)]·DMF 5 was isolated as a minor compound. Compound 5 has a two-dimensional structure, with Cd-Hbtc zig-zag chains linked into sheets through the pyrazine ligands.