A 3D copper(II)-sodium(I)-containing Strandberg-type phosphomolybdate-based coordination framework with a flexible bis(triazole) ligand: Synthesis, crystal structure and catalytic properties

An unusual Cu(II)-Na(I)-containing Strandberg-type phosphomolybdate-based MOF with a flexible bis(triazole) ligand was synthesized by using the ionic liquid EMIm-Br as template and employed to catalyze the solvent-free ring-opening polymerization of ε-caprolactone. [Display omitted] •A novel Cu(II)-Na(I)-containing Strandberg-type POM-based MOF is synthesized.•An unprecedented anionic POM-based MOF with sqc topology is demonstrated.•Catalytic solvent-free ROP of ε-caprolactone over the CZU-6 catalyst is presented. A new copper(II)-sodium(I)-containing phosphomolybdate-based coordination framework, namely, {[EMIm][Cu1.5Na(btmx)2.5(H2O)2(HP2Mo5O23)]·0.5H2O}n (denoted as CZU-6, EMIm = 1-methyl-3-ethyl imidazolium, btmx = 1,4-bis(1,2,4-triazole-1-ylmethyl)-2,3,5,6-tetramethyl benzene), was synthesized by using ionic liquid EMIm-Br as a template under hydrothermal conditions. The X-ray structural analysis revealed that CZU-6 features the first example of 3D anionic polyoxometalate-based coordination framework with trinodal (4,4,4)-connected sqc topological net. Moreover, CZU-6 could be directly adopted as an efficient heterogeneous catalyst for the solvent-free ring-opening polymerization of ε-caprolactone, and the catalyst could be easily recovered and reused several times without loss of its crystallinity and activity.