Two Polyoxophosphotungstates Formed by Wells−Dawson Cores Linked through W−O−W Linkages

Abstract

Two polyoxophosphotungstates, [Hen][Cu(en)2(H2O)]2[Cu(en)2(H2O)2]0.5[{Cu(en)2(H2O)}2 {Cu(en)2}(P2W18O61)2]·en·nH2O (en = ethylenediamine, n = 16.35), 1, and [HenMe]2 [Cu(enMe)2][{Cu(enMe)2}P2W18O61]·9H2O (enMe = 1,2-diaminopropane), 2, have been synthesized under hydrothermal conditions. It was revealed that two Wells−Dawson cores in 1 are condensed through sharing two common O atoms into an unprecedented polyoxometalate dimer in a belt-to-belt fashion, which are further fused by a copper(II) bridging fragment and grafted by two copper(II) complexes. Every two polyoxometalate units in 2 are interconnected through an oxo and a complex bridged linkers into a chainlike structure. It suggested that the pH value of the reactive mixture and the steric interference of the methyl group of enMe ligand play crucial roles on the resultant structures. Compounds 1 and 2 represent the first condensed structures formed by unsubstituted POM clusters through sharing common atoms. Along with well-separated Cu2+ centers, their magnetic behaviors can be explained based on tetranuclear and dinuclear antiferromagnetic coupling models, respectively. It was indicated that the compounds have catalytic activity in epoxidation of maleic anhydride