Extended Members of the Layered Rare-Earth Hydroxide Family, RE2(OH)5NO3•nH2O (RE = Sm, Eu, and Gd): Synthesis and Anion-Exchange Behavior

Three new layered rare-earth hydroxides (LRHs), RE(OH)(2.5)(NO3)(0.5)center dot xH(2)O (RE = Gd, Eu, and Sm), have been prepared by a hydrothermal reaction. These materials correspond to the extended members of the RE2(OH)(5)NO3 center dot nH(2)O (RE = the rare-earth series) family. Although it has been suggested that the LRH structure seems to be kinetically favored by yttrium or (the second half of) the small rare-earth ions, an appropriate control of pH conditions for the hydrothermal reaction could extend this family to the larger rare-earth ions in the present study. The ion-exchange reactions between NO3- and diverse organic anions (a series of organic carboxylates, 1-alkanesulfonates, and alkylsulfates) were successfully carried out in the gallery of layered rare-earth hydroxides, RE2(OH)(5)NO3 center dot nH(2)O (RE = Gd, Eu, and Sm). The FTIR spectra of the LRH hosts and some selected organic anion-exchanged derivatives clearly revealed the absence of nitrate and the appearance of characteristic bands attributed to carboxylate and sulfonate groups after the exchange reactions. Despite a large expansion of interlayer spacing, the layered gadolinium hydroxide and the long alkyl chain anion-exchanged derivative showed a similar paramagnetic behavior. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)