Tuning the architectures of polyoxometalate-templated complexes by changing the spacer lengths of bis-pyridyl-bis-amide ligands (L): from 1D chains to 2D networks based on different (CuL)n loops

A series of metal-organic complexes based on Keggin-type polyoxometalate (POM) templates and bis-pyridyl-bis-amide ligands with tuned spacer lengths have been hydrothermally synthesized and structurally characterized: [Cu-2(L-1)(3)(SiMo12O40)(H2O)(6)]center dot 2H(2)O (1), [Cu-2(L-2)(3)(SiMo12O40)(H2O)(6)]center dot 9H(2)O (2), [Cu-2(L-2)(3)(SiW12O40)(H2O)(6)]center dot 6H(2)O (3), [Cu-2(L-3)(3)(SiMo12O40)(H2O)(6)]center dot 4H(2)O (4) and [Cu-2(L-3)(3)(SiW12O40)(H2O)(6)]center dot 4H(2)O (5) [L-1 = N,N'-bis(3-pyridinecarboxamide)-1,2-ethane, L-2 = N,N'-bis(3-pyridinecarboxamide)-1,4-butane, L-3 = N,N'-bis(3-pyridinecarboxamide)-1,6-hexane]. Single-crystal X-ray analyses reveal that compound 1 is a two-dimensional (2D) supramolecular structure based on one-dimensional (1D) infinite chains containing quadrate Cu-2(L-1)(2) loops and Keggin polyanion templates. Compounds 2 and 3 are isostructural, and they display unusual 1D -> 2D poly-rotaxane frameworks containing large square Cu-2(L-2)(2) loops, in which the Keggin polyanions are sandwiched between the parallel-packed 2D sheets. Compounds 2 and 3 represent the first POM-templated 2D metal-organic poly-rotaxane networks. Compounds 4 and 5 are isostructural, and they exhibit a 2D metal-organic architecture based on Cu-6(L-3)(6) loops which are large enough to accommodate two Keggin polyanions, in which the polyanions are sandwiched among the stagger-packed cationic sheets. Compounds 1-5 represent examples of introducing flexible bis-pyridyl-bis-amide ligands into POM systems. The electrochemical properties of compounds 1 and 3 and the photocatalytic properties of the title compounds have been reported.