Solid-state and solution studies of {Lnn(SiW11O39)} polyoxoanions:: An example of building block condensation dependent on the nature of the rare earth

The reactivity of the [alpha-SiW11O39](8-) monovacant polyoxometalate with lanthanide has been investigated for four different trivalent rare-earth cations (Ln = Nd-III, Eu-III, Gd-III, Yb-III). The crystal structures of KCs4[Yb(alpha-SiW11O39)(H2O)(2)].24H(2)O (1), K0.5Nd0.5[Nd-2(alpha-SiW11O39)(H2O)(11)].17H(2)O (2a), and Na0.5Cs4.5[Eu(alpha-SiW11O39)(H2O)(2)].23H(2)O (3a) are reported. The solid-state structure of compound 1 consists of linear wires built up of [alpha-SiW11O39](8-) anions connected by Yb3+ cations, while the linkage of the building blocks by Eu3+ centers in 3a leads to the formation of zigzag chains. In 2a, dimeric [Nd-2(alpha-SiW11O39)(2)(H2O)(8)](10-) entities are linked by four Nd3+ cations. The resulting chains are connected by lanthanide ions, leading to a bidimensional arrangement. Thus, the dimensionality, the organization of the polyoxometalate building units, and the Ln/[alpha-SiW11O39](8-) ratio in the solid state can be tuned by choosing he appropriate lanthanide. The luminescent properties of compound 3a have been studied, showing that, in solution, the polymer decomposes to give the monomeric complex [Eu(alpha-SiW11O39)(H2O)(4)](5-). The lability of the four exogenous ligands connected to the rare earth must allow the functionalization of this lanthanide polyanion.