The supramolecular assembly of a series of covalently modified Anderson-type polyoxometalates (POMs) and 18-crown-6 ethers was investigated for the first time. Seven new POM–crown ether complexes were prepared by varying the countercations and the modification mode of the Anderson clusters, and they were fully characterized by single-crystal X-ray diffraction, electrospray ionization time-of-flight mass spectrometry (ESI–TOF–MS), ¹H nuclear magnetic resonance (NMR), etc. Alkali metal cations within the cavities of the crown ethers served as supercations to bind to the POM hybrids, thereby forming supramolecular assemblies with different architectures and compositions. More interestingly, five of the seven POM–crown ether complexes possessed novel pseudo-rotaxane structures, which were obtained by changing the modification mode of the Anderson clusters from symmetric to asymmetric. These pseudo-rotaxanes have not been reported previously and are considered important intermediates in the construction of POM-based supramolecular architectures with complementary structural and chemical properties.

Indium-based materials (e.g., In₂O₃) are a class of promising non-noble metal-based catalysts for electroreduction of carbon dioxide (CO₂). However, competitive hydrogen reduction reaction (HER) on indium-based catalysts hampers CO₂ reduction reaction (CO₂RR) process. We herein tune the interfacial microenvironment of In₂O₃ through chemical graft of alkyl phosphoric acid molecules using a facile solution-processed strategy for the first time, which is distinguished from other researches that tailor intrinsic activity of In₂O₃ themselves. The surface functionalization of alkyl phosphoric acids over In₂O₃ is demonstrated to remarkably boost CO₂ conversion. For example, octadecylphosphonic acid modified In₂O₃ exhibits Faraday efficiency for H₂ (FE ${}_{{\mathrm{H}}_2}$) of as low as 6.6% and FE_HCOOH of 86.5% at −0.67 V vs. RHE, which are far superior to parent In₂O₃ counterparts (FE ${}_{{\mathrm{H}}_2}$ of 24.0% and FE_HCOOH of 63.1%). Moreover, the enhancing effect of alkyl phosphoric acid functionalization is found to be closely related to the length of alkyl chains. By virtue of comprehensive experimental characterizations and molecular dynamics simulations, it is revealed that the modification of alkyl phosphoric acids significantly alters the interface microenvironment of the electrocatalyst, which changes the electrocatalyst surface from hydrophilic and aerophobic to hydrophobic and aerophilic. In this case, the water molecules are pushed away and more CO₂ molecules are trapped, increasing local CO₂ concentration at In₂O₃ active sites, thus leading to the significantly enhanced CO₂RR and suppressed HER. This work highlights the importance of regulating the interfacial microenvironment of inorganic catalysts by molecular surface functionalization as a means for promoting the electrochemical performance in electrosynthesis and beyond.

Covalently modified polyoxometalates (POMs), which benefit from the synergistic effect between POMs and covalently grafted moieties, have received increasing attention in various fields. Recent studies on covalently modified POMs mainly focus on function-directed POM assemblies. This review summarizes the latest progress (2017–2022) concerning covalently modified POMs from a functional perspective, which can be classified as assembly chemistry, photochemistry, electrochemistry, homogeneous and heterogeneous catalysis, and biological applications. The roles of POMs and covalently grafted moieties in these hybrids, especially the rational design for specific applications, were considered and emphasized.