Double-malate bridging tri-lanthanoid cluster encapsulated arsenotungstates: syntheses, structures, luminescence and magnetic properties.

Five members of a new family of polyoxometalate (POM)-ligated trinuclear lanthanoid (Ln) clusters with the general formula K20Li2[Ln3(μ3-OH)(H2O)8(AsW9O33)(AsW10O35(mal))]2·17H2O [Ln = Dy (1Dy), Tb (2Tb), Gd (3Gd), Eu (4Eu), and Sm (5Sm), mal = malate] have been synthesized, all of which consist of the dimeric {[Ln3(μ3-OH)(H2O)8(AsW9O33)[AsW10O35(mal)]}(11-) polyanion constructed from a {AsW9O33} and a {AsW10O35(mal)} building block linked by a tri-Ln cluster [Ln3(μ3-OH)(H2O)8](8+), where the two malate ligands play a key bridging role. The {AsW10O35(mal)} subunit can be viewed as the {AsW9O33} building block anchoring an additional tungsten center [WO2(mal)]. The electrospray ionization mass (ESI-MS) spectra indicate that the dimeric fragments of 1Dy and 2Tb are unstable, which are apt to produce the subunit [KH5Ln3(OH)(H2O)(AsW9O33)2](4-) in solution. The solid-state photoluminescence measurements display the yellowish green emission for 1Dy and 5Sm, green emission for 2Tb and reddish orange emission for 4Eu, which are attributed to the Ln(III) f-f electron transitions. Magnetic property studies indicate that 1Dy displays probable SMM behaviour with slow magnetization relaxation, whereas the weak antiferromagnetic interactions exist in two {Ln3} clusters for 2Tb-5Sm.