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

Abstract

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.