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

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-((PMo11MoO40)-Mo-VI-O-V)(H2O)(2)]center dot 2H(2)O (1), [Cu2L2((PW11WO40)-W-VI-O-V)(H2O)(6)]center dot H2O (2), [Cu2L2(SiW12O40)(H2O)(6)]center dot 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 [(PMo11MoO40)-Mo-VI-O-V](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 mu(3)-bridging coordination mode (via ligation of two pyridyl nitrogen atoms and one carbonyl oxygen atom) in 1 and 4, and a mu(2)-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.