A feasible route to approach 3D POM-based hybrids: utilizing substituted or reduced Keggin anions with high charge density

Abstract

Five new hybrid compounds based on Keggin polyanions, Ag⁺/Cu⁺ ions and 1,3-bis(1,2,4-triazol-1-yl)propane (btp) molecules have been hydrothermally synthesized. In [Ag₅(btp)₄(H₂O)₂][PCuW₁₁O₃₉]·2H₂O (1), [Ag_4.33Na_0.67(btp)₄(H₂O)₂][PMnMo₁₁O₃₉]·H₂O (2) and [Cu₄(btp)₄Na(H₂O)₂][PMnMo₁₁O₃₉]·2H₂O (3), the neighboring mono-substituted Keggin clusters are alternately connected via sharing oxygen atoms to form an unusual Keggin-based transition-metal monosubstituted chain, in which the Keggin cluster serves as a decadentate ligand and grafts ten metal atoms representing the highest connected number for Keggin cluster and forming a 3D framework. In [Ag₅(btp)₄][PW^VI₁₀W^V₂O₄₀] (4) and [Ag₅(btp)₄][PMo^VI₁₀Mo^V₂O₄₀] (5), two-electron reduced Keggin clusters as hexadentate linkages are inserted in the rhomboid-like tunnels of the Ag-btp framework and connect with the framework via six Ag–O bonds to achieve 3D motifs, which are new and rare examples of heteropoly blue based hybrid compounds. The successful synthesis of the five high-dimensional structures may provide a feasible route for us to approach 3D polyoxometalate-based hybrids by using substituted Keggin anions and heteropoly blues with high charge density. Furthermore, photocatalytic experiments indicate that both 1 and 4 have good activities for photocatalytic degradation of RhB under UV irradiation. The luminescent properties of compounds 1–5 in the solid state were also investigated.