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

Abstract

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: [Cu2(L1)3(SiMo12O40)(H2O)6]·2H2O (1), [Cu2(L2)3(SiMo12O40)(H2O)6]·9H2O (2), [Cu2(L2)3(SiW12O40)(H2O)6]·6H2O (3), [Cu2(L3)3(SiMo12O40)(H2O)6]·4H2O (4) and [Cu2(L3)3(SiW12O40)(H2O)6]·4H2O (5) [L1 = N,N′-bis(3-pyridinecarboxamide)-1,2-ethane, L2 = N,N′-bis(3-pyridinecarboxamide)-1,4-butane, L3 = 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 Cu2(L1)2 loops and Keggin polyanion templates. Compounds 2 and 3 are isostructural, and they display unusual 1D→2D poly-rotaxane frameworks containing large square Cu2(L2)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 Cu6(L3)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.