Two Keggin-Based Isostructural POMOF Hybrids: Synthesis, Crystal Structure, and Catalytic Properties

Abstract

In this work we synthesized two novel isostructural twin hybrids Comp1: [H(CHN)Cu][PMoO] & Comp2: [H(CHN)Cu][PWO], based on the Keggin ions (PMoO & PWO), Cu(I) cation, and 4,4'-bipyridine, by in situ hydrothermal reduction of Cu, facilitated through extensive standardizations of synthetic pH conditions. Both compounds crystallized in monoclinic P2/ c space group with similar lattice parameters and crystal structures. The structural similarity prompted us to explore comparative catalytic properties of the hybrids, to understand the relative role of the POM species in the activity. While characterization techniques like powder X-ray diffraction (XRD), single-crystal XRD, IR, adsorption studies, etc. confirmed the identical structural hierarchy in the twin polyoxometalate-based metal organic frameworks (POMOFs), critical analyses through X-ray photoelectron spectroscopy, X-ray absorption near-edge structure spectroscopy, and magnetic property studies elucidated the electronic and local structural properties of the two. The hybrids were highly active for heterogeneous catalysis of small-molecule oxidation, with Comp 2 showing better activity than Comp1, particularly for oxidation of ethylbenzene and cyclooctene. Comp2 also outperformed Comp1 in photocatalytic degradation of methylene blue, with higher conversion efficiency of 83% and one order higher apparent rate constant of 0.0139 min, which is comparable to that of the well-known photocatalyst, P25. Electrochemical pseudocapacitance studies revealed that these POMOFs are having the potential to act as good charge storage and conducting devices if their electrochemical stability can be improved.

POM@MOF Hybrids: Synthesis and Applications

“…Recently, this group also prepared the PV2Mo10@NU-1000 catalyst by using the same method and the synthesized material showed a full conversion of CEES, with O2 as the oxidant. In addition to the well-known MOFs, several other POM@MOF hybrid materials, including [Co(BBPTZ)3][HPMo12O40]•24H2O and [Cu I 6(trz)6(PW12O40)2], have been synthesized and applied for ODS [88], the oxidation of aryl alkenes [89,90], alkylbenzenes [91], and alcohols [92] (see Table 2).…”

Two rare {M2(MoO4)2}n chain-containing molybdate-based metal–organic complexes with a bis-pyrazole-bis-amide ligand: fluorescent sensing and photocatalysis performance

“…For example, Peter's group reported two new isostructural polyoxomolybdate-based metal organic complexes whose photocatalytic degradation efficiency for MB was 57% and 83%, respectively. 46 The possible mechanism of the photocatalytic activity was derived as follows: POM was induced to shi from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) under UV irradiation. The excited state of POM* was generated during this period, accompanied by the formation of H + , $OH, and $O 2 À , which can inactivate the organic dye during the oxidation process, thereby realizing the photocatalytic process.…”

Three novel polyoxometalate-based inorganic–organic hybrid materials based on 2,6-bis(1,2,4-triazol-1-yl)pyridine

“…Therefore, the photocatalytic properties of POMs have a wide range of potential applications in purifying water quality. 43 Herein, Rhodamine B (RhB) was used to investigate the photocatalytic performance of compounds 1-3 upon UV irradiation from a 300 W Hg lamp. Moreover, the photodegradation process of RhB without catalyst has also been studied under the same conditions (Fig.…”