Synthesis and structure of the first dinuclear lanthanide oxalato complexes [{MoV2O4(C2O4)2(H2O)2}2{(Ln2(H2O)4)2(C2O4)}]·7H2O (Ln=La3+,Ce3+)

Reaction between the [MoV2O4(H2O)2(C2O4)2]2− anion and LnIII (Ln=La,Ce) in water affords the isostructural neutral complexes [{MoV2O4(C2O4)2(H2O)2}2{(Ln2(H2O)4)2(C2O4)}]. The structures have been solved by single-crystal X-ray diffraction and consist in a heteronuclear six-membered ring encapsulating an oxalate anion which connects the two rare earth cations. The formation of these complexes implies a partial decomposition of the precursor due to the high affinity of lanthanide toward oxalate in water which prevents the formation of analogous compounds with heavier rare earth cations in aqueous media.