Syntheses, Crystal Structure, Electrocatalytic, and Magnetic Properties of the Monolanthanide-Containing Germanotungstates [Ln(H2O) n GeW11O39]5- (Ln = Dy, Er, n = 4,3).

Masooma Ibrahim,Yan Peng,Anthony B Carter,Pedro De Oliveira,Ananya Baksi,Thomas Bergfeldt,Israël M Mbomekallé,Sharali Malik,Christopher E Anson

doi:10.1021/acsomega.9b02846

Abstract

Two monolanthanide-containing polyanions based on monolacunary Keggin germanotungstates [Ln(H2O)nGeW11O39]5– (Ln = Dy, Er, n = 4,3) have been synthesized in simple one-pot synthetic procedure and compositionally characterized in solid state by single-crystal X-ray diffraction, powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and elemental analysis. Electronic absorption and emission spectra of the title compounds in solution were also studied. The [DyIII(H2O)4GeW11O39]5– Keggin POM exhibits a slow relaxation of magnetization. The cyclic voltammetry measurements and mass spectrometry were carried out to check the stability of the compounds in solution. Both polyanions prove efficient in the electrocatalytic reduction of nitrite. To our knowledge, this observation establishes the first example of electrocatalysis of nitrite reduction by all inorganic monolanthanide-containing germanotungstates family.

Highlights

Polyoxometalates (POMs) are discrete metal oxygen cluster anions constructed from early transition metals (M = V, Nb, Ta, Mo, W) in their highest oxidation state and are being extensively studied because of their application in catalysis, energy, molecular magnetism, biochemistry, optics, and separation science.1−16 Lacunary POM ligands are versatile inorganic building blocks for the construction of moleculebased materials
Two monolanthanide-containing polyanions based on monolacunary Keggin germanotungstates [Ln(H2O)nGeW11O39]5− (Ln = Dy, Er, n = 4,3) have been synthesized in simple one-pot synthetic procedure and compositionally characterized in solid state by single-crystal X-ray diffraction, powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and elemental analysis
The morphology of the isolated POM crystals were investigated by scanning electron microscopy (SEM)

Summary

Introduction

Polyoxometalates (POMs) are discrete metal oxygen cluster anions constructed from early transition metals (M = V, Nb, Ta, Mo, W) in their highest oxidation state and are being extensively studied because of their application in catalysis, energy, molecular magnetism, biochemistry, optics, and separation science.− Lacunary POM ligands are versatile inorganic building blocks for the construction of moleculebased materials. The structural varieties and functionalities of these materials could be tuned by the incorporation of different transitionmetal ions,− rare earth (RE) metal cations,− and mixed TM−RE metal centers.− Lanthanide cations with high coordination number are generally considered as suitable linkers for linking POM fragments into discrete nanosized POM frameworks or extended structures. In the field of molecular magnetism, lanthanide ions (typically Tb, Dy, Ho, and Er) are investigated for the search of singlemolecule magnets (SMMs) with a high blocking temperature due to their usual large magnetic moments and large magnetic anisotropy. Single-molecule magnets are individual high-spin molecules displaying a slow spin relaxation and preserving their magnetic moment below the characteristic blocking temperature (TB). Interestingly, [ErW10O36]9− is the first polyoxometalate behaving as a single-molecule magnet (SMM) and can be considered as a molecular analogue of classical bulk ferromagnet. Regarding the advances of POMs in catalysis, the most fascinating properties of POMs in the Received: September 3, 2019 Accepted: November 18, 2019 Published: December 10, 2019

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