A novel-type mixed-ligand polyoxotungstolanthanoate, [Ln(BW11O39)(W5O18)]12- (Ln = Ce3+ and Eu3+)

Two isostructural anions, [Ln(BW11O39)(W5O18)](12-) (Ln = Ce and Eu), were isolated as K+ salts from aqueous solutions containing tungstate, Ln(3+), and BO33-, at pH = 7. An X-ray crystallographic analysis showed that the Ln(3+) center in the anion is chelated by two kinds of tetradentate polyoxotungstate ligands, [W5O18](6-) and alpha-[BW11O39](9-) with a square antiprismatic LnO(8) configuration, which are monovacant derivatives of [W6O19](2-) and alpha-[BW12O40](5-), respectively. The anion is of approximate C-s symmetry, and the observable asymmetry of K-O bonding between two different K+ cations and the anion causes the two mirror planes within [(W5O18)Ln](3-) and [(BW11O39)Ln](6-) moieties to be canted to each other by 5.2 degrees for Ln = Ce and 4.1 degrees for Ln = Eu.