Four POM-based complexes modified by multi-nuclear clusters: structure, photocatalytic, supercapacitor and chromogenic properties

Abstract

Four POM-based complexes were synthesized under hydrothermal conditions by using two kinds of triazole derivatives, namely [Cu₂(Cmt)₂(OH)Cl(β-Mo₈O₂₆)_0.5] (1), [Cu(H₂O)₃(H_3/2Tpm)₂](HTpm)(PMo₁₂O₄₀)₂·4H₂O (2), [Cu₃Cl₂(H₂Tpm)₂(HTpm)₄(PMo₁₂O₄₀)₄]·26H₂O (3), and [Co₃(HTpm)₆(H₂O)₂(Mo₁₃O₄₂)₂]·21H₂O (4) (Cmt = 1-cyclopropylmethyl-1-H-[1,2,4]triazole, Tpm = 4-(3-[1,2,4]triazole-4-propyl)morpholine). Complex 1 contains tetra-nuclear Cu clusters, which are linked by Mo₈ anions to form a 1D chain. Both complexes 2 and 3 are 0D structures, and complex 3 includes tri-nuclear Cu clusters. Rarely observed [Mo₁₂O₃₈]⁴⁻ subunits are present in complex 4, which are further linked by {MoO₄} to construct a new infinite Mo–O chain. These Mo–O chains are connected by tri-nuclear [Co₃(HTpm)₆(H₂O)₂]¹²⁺ clusters to build the 3D framework of 4. Complexes 1–4 exhibit good electrochemical properties and can be used as amperometric sensors for detection of Cr(VI), NO₂⁻, H₂O₂ and Fe(III). Complexes 1 and 2 have good capacitance performance. In particular, at a current density of 1 A g⁻¹, the specific capacitance of complex 2 is as high as 1618 F g⁻¹. Complexes 1–4 have photocatalytic activity, and can not only photocatalyze the degradation of organic dyes, but also photocatalyze the reduction of Cr(VI). In addition, complexes 2 and 4 exhibit photochromic and thermochromic properties.