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Rare Earth Arenedisulfonate Metal−Organic Frameworks:  An Approach toward Polyhedral Diversity and Variety of Functional Compounds

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posted on 30.04.2007, 00:00 by Felipe Gándara, Alberto García-Cortés, Concepción Cascales, Berta Gómez-Lor, Enrique Gutiérrez-Puebla, Marta Iglesias, Angeles Monge, Natalia Snejko
Eight 2D and 3D metal−organic framework (MOF) rare earth naphthalenedisulfonates have been obtained. The different geometry of the naphthalenedisulfonic acids used as connectors [(1,5-NDS) and (2,6-NDS)] gives rise to the three new structure types. In Ln(OH)(1,5-NDS)H2O, LnPF-1 (lanthanide polymeric framework; Ln = La, Nd, Pr, Sm and Eu), the lanthanide ion is octacoordinated. Its 3D structure is formed by (Ln2O14)−S−(Ln2O14) infinite chains, connected through complete NDS connectors. LnPF-2 (Ln = Nd), with the same empirical formula as the former, and the lanthanide in octa- and nonacoordination, owns an arrangement of sulfonate bridges and neodymium polyhedra that gives rise to a 2D structure. [Ln5(2,6-NDS)3(OH)9(H2O)4](H2O)2, LnPF-3 (Ln = Nd, Eu), demonstrates that it is possible to obtain a 3D structure with (2,6-NDS), when a greater Ln/connector ratio is employed. It is worth pointing out the existence, in this latter family of compounds, of a μ5-OH group, whose hydrogen atom is very close to one-sixth Ln atom (distance Ln···H = 2.09 Å). The materials, with high thermal stability, act as active and selective bifunctional heterogeneous catalysts in oxidation of linalool yielding cyclic hydroxy ethers. The absence of any 3D Nd−Nd magnetic interaction is explained due to the inner nature of 4f orbitals of Nd3+, which do not favor the magnetic exchange. The influence of the polymeric frame matrix results in a better photoluminescence efficiency for NdPF-1.