Two mixed-addenda Nb/W polyoxometalate-based hybrid compounds containing multicopper units: synthesis, structures, and electrochemical and magnetic properties

Abstract

Two mixed-addenda Nb/W polyoxometalate (POM)-based hybrid compounds, [Cu^ICu(μ₃-OH)(H₂O)₆(trz)₃]₂(PW₉Nb₃O₄₀)·13H₂O (1) and [Cu^ICu(μ₃-OH)(H₂O)₄(Htrz)(trz)₃]₂(PW₉Nb₃O₄₀)·13H₂O (2), were synthesized under hydrothermal conditions. Single-crystal X-ray diffraction revealed that compound 1 contains planar triangular tricopper {Cu(μ₃-OH)(trz)₃} units, and these tricopper units link to each other to form a 1D anti-parallel chain. Cu^I ions connect the 1D chains by the coordination of trz ligands to form 2D layers in the ab plane. Compound 2 contains the same tricopper {Cu(μ₃-OH)(trz)₃} units as well as bicopper {Cu(Htrz)₂} units. The tricopper units also form 1D chains and the bicopper units connect the 1D chains to form similar 2D layers and finally construct the 3D framework. In both compounds, each Nb/W mixed-addenda Keggin {PW₉Nb₃O₄₀} unit links eight tricopper units to generate the final 3D structure. Magnetism studies indicate anti-ferromagnetic exchange interactions among the Cu^II ions within the tricopper units, with J_Cu-Cu values of -209.3 and -200.8 cm^-1 in 1 and 2, respectively.