A series of Anderson-type polyoxometalate-based metal–organic complexes: their pH-dependent electrochemical behaviour, and as electrocatalysts and photocatalysts

Abstract

Seven polyoxometalate-based (POM) metal-organic complexes (MOCs) with different pyridyl-amide ligands were hydrothermally synthesized and structurally characterized. In 1, the [CrMo6(OH)5O19](4-) (CrMo6) polyoxoanions bridge the Cu(II) ions to generate a 1D Cu-CrMo6 inorganic double chain, which is further consolidated by the μ2-bridging 2-pdya ligands. Complex 2 exhibits a 2D layer based on [γ-Mo8O26]n(4n-) chains. In complex 3, the β-Mo8O26 anions link the metal-organic units [Cu(4-Hdpyp)2](4+) to construct a 1D fishbone-like chain. Complex 4 shows a 3D (6,6)-connected framework constructed by the 2D inorganic network [Cu4(μ3-OH)2(H2O)4(γ-Mo8O27)] and 3-dpyh bridging ligands. In 2-4, all the [CoMo6(OH)6O18](3-) (CoMo6) anions were in situ transformed to Mo8O26(4-) or Mo8O27(6-) anions. Complexes 5 and 7 are isostructural, each [TeMo6O24](6-) (TeMo6) polyoxoanion coordinates to two Cu(II) ions to generate a discrete copper complex [Cu2(4-Hdpye)2(TeMo6O24)(H2O)6] and [Cu2(4-Hdpyb)2(TeMo6O24)(H2O)6], respectively. In complex 6, the TeMo6 polyoxoanions bridge the Cu(II) ions to generate a 2D [Cu3(TeMo6)]n inorganic layer, which is further linked by the μ2-bridging 3-dpyb ligands to form a 3D metal-organic framework. The effects of POM types and their various coordination modes, as well as the pyridyl-amide ligands on the structures of the title complexes have been discussed. Their electrochemical behavior reveals characteristic multi-electron redox processes related to Mo(VI) centers. The electrocatalytic reduction performance toward hydrogen peroxide and bromate was fully measured and discussed; both complexes exhibit excellent electrocatalytic activity towards the reduction of bromate and hydrogen peroxide. In addition, the redox potentials of complexes 5-7 are highly pH sensitive and may be used as a kind of potential pH sensor. The photocatalytic activities of the title complexes are also investigated in detail.

Experimental and Theoretical Investigation of the Light‐Driven Hydrogen Evolution by Polyoxometalate–Photosensitizer Dyads

“…Thus, in contrast to the well‐documented reactivity of metal‐functionalized lacunary Keggin and Lindqvist anions, little is known about the effects of metal substitution in the Anderson anion. This information, however, is critical as metal exchange is expected to significantly affect the electronic structure of the anion and thus its reactivity in redox and light‐driven processes …”

Hourglass-Type Polyoxometalate-Based Crystalline Material as an Efficient Proton-Conducting Solid Electrolyte

“…New peaks appear and the previous three pairs of peaks are replaced (Figure ). This phenomenon is attributed to the reduction of H 2 O 2 in the electrolyte . The CV curves of {P 4 Mo 6 }-CPE in the electrolytes H 2 SO 4 , Na 2 SO 4 , and 12 mmol/L H 2 O 2 are shown in Figure c.…”

A New Anderson‐Type Polyoxometalate‐Based Metal‐Organic Complex for Multi‐Functional Electrochemical Application

“…At 3400 cm À 1 , the band is attributed to the presence of water molecules. [38] For the X-ray powder diffraction pattern and thermogravimetric analysis of the sample of complex 1, please refer to the support information and Figure S2-S3 for details. (all data) 0.2198 Largest diff.…”