Effect of polyoxoanions and amide group coordination modes on the assembly of polyoxometalate-based metal–organic complexes constructed from a semi-rigid bis-pyridyl-bis-amide ligand

Abstract

A series of polyoxometalate (POM)-based metal–organic complexes constructed from a semi-rigid bis-pyridyl-bis-amide ligand have been hydrothermally synthesized and structurally characterized: [Cu₂L₂(PMo^VI₁₁Mo^VO₄₀)(H₂O)₂]·2H₂O (1), [Cu₂L₂(PW^VI₁₁W^VO₄₀)(H₂O)₆]·H₂O (2), [Cu₂L₂(SiW₁₂O₄₀)(H₂O)₆]·H₂O (3) and [Cu₂L₂(H₂K₂Mo₈O₂₈)(H₂O)₂] (4) (L = N,N′-bis(3-pyridinecarboxamide)-piperazine). Single-crystal X-ray analyses reveal that complex 1 is a 2D metal–organic architecture based on the Keggin-type [PMo^VI₁₁Mo^VO₄₀]⁴⁻ anions and quadrate Cu₂L₂ loops. Isostructural complexes 2 and 3 display 2D supramolecular networks based on 1D infinite chains, which are constructed from quadrate Cu₂L₂ loops and Keggin polyoxoanions. Complex 4 exhibits a 3D metal–organic framework derived from the newly-reported [K₂Mo₈O₂₈]⁶⁻ polyoxoanions and quadrate Cu₂L₂ loops. The L ligands show a μ₃-bridging coordination mode (via ligation of two pyridyl nitrogen atoms and one carbonyl oxygen atom) in 1 and 4, and a μ₂-bridging coordination mode (via ligation of two pyridyl nitrogen atoms) in 2 and 3, forming Cu₂L₂ loops in 1–4. The influence of amide group coordination modes and structural features of POMs on the structures of the title complexes has been discussed. The electrochemical properties and selective photocatalytic properties of the title complexes have been reported in this article.