Metal Ion and Metal-to-Ligand Ratio Regulated Construction of Cu(II) and Co(II) Coordination Polymers as Efficient Catalysts for Ring-Opening Polymerization of L-Lactide

Three new coordination polymers (CPs), {[Cu(NDC)(Fbtx)(H2O)] & sdot; 1.5H(2)O}(n) (1), {[Co(NDC)(Fbtx)(H2O)(2)] & sdot; 0.5Fbtx}n (2), and [Co-2(NDC)(2)(Fbtx)](n) (3), were synthesized by employing acid-base mixed ligands of rigid 1,4-naphthalenedicarboxylic acid (H2NDC) and flexible bis(1,2,4-triazole-1-ylmethyl)-2,3,5,6-tetrafluorobenzene (Fbtx) under both hydrothermal and microwave-assisted reaction conditions. Single-crystal structure analysis establishted that both compounds 1 and 2 exhibit two-dimensional (2D) layered structures, while compound 3 features a three-dimensional (3D) complicated framework. The geometries of metal ions vary from square pyramidal (in 1 and 3) to distorted octahedral (in 2). Topological strudy showed that compounds 1 and 2 have exposed common 4-connected 4(4)-sql net, while compound 3 has made a novel 4,5-connected net with point symbol of (4(3) & sdot; 6(2) & sdot; 7)(4(3) & sdot; 6(4) & sdot; 7(2) & sdot; 8). The catalytic performance of the three complexes for the solvent-free ring-opening polymerization of L-lactide has been investigated. The results indicated that compound 3 with coordinatively unsaturated cobalt(II) sites showed good activity and the molecular weight of the polymer obtained was high. Moreover, the complex 3 catalyst could be recycled up to five times with the retention of both catalytic activity and crystal structure.