Construction of 3D metal–organic frameworks bearing heteropolyoxometalate units and multi-azole molecules and exploration of their photocatalytic activities

Taking advantage of multi-azole molecules as organic linkers, two novel 3D metal–organic frameworks consisting of heteropolyoxometalate building blocks, i.e., [Cu5(1,4-ttb)4(CrMo6(OH)6O18)(H2O)8]·10H2O (1) and [Cu4(1,4-ttb)4(SiW12O40)(H2O)8]·4H2O (2) (1,4-ttb = 1-(tetrazo-5-yl)-4-(triazo-1-yl)benzene) have been fabricated and characterized via X-ray single-crystal diffraction, FT-IR spectroscopy, powder X-ray diffraction (PXRD) and TG analyses. Compounds 1 and 2 both possess pillared-layer 3D frameworks which were based on POM units and different Cu–tetrazolate motifs. Compound 1 is a (2,6,6)-connected 3D framework constructed from the 2D networks {Cu5(1,4-ttb)4(H2O)8}n through connected CrMo6 polyoxoanions with (32.42.52.68.8)(34.44.54.63) topology. Compound 2 is a (2,3,5)-connected 3D framework constructed from the 2D wave layers {Cu4(1,4-ttb)4(H2O)8} through connected SiW12 polyoxoanions with (4.82)2(42.64.82.102)(8) topology. Magnetism studies of compound 1 reveal the dominant antiferromagnetic coupling between the Cu(II) ions. The electrochemistry properties of compound 2 were studied. Intriguingly, compounds 1 and 2 display considerable photocatalytic activities for the degradation of several organic dyes.