Observation and Isolation of Layered and Framework Ytterbium Hydroxide Phases Using In Situ Energy-Dispersive X-ray Diffraction

In situ energy-dispersive X-ray diffraction has been used to investigate the synthesis of the recently reported lanthanide hydroxynitrate phases, Ln(2)(OH)(5)NO3 center dot 1 5H(2)O (Ln = Y, Er, Yb) Through control of the reaction temperature, three distinct layered phases with differing degrees of hydration (x = 1 (1), 1 5 (2), and 2 (3)) were observed in the Yb synthesis and subsequently isolated Only the phase with x = 1 5 was observed for the reactions with Y and Er The crystal structures of Yb-2(OH)(5)NO3 center dot 2H(2)O (2) and Yb-2(OH)(5)NO3 center dot H2O (3) were determined in a single-crystal diffraction study and represent the first crystal structures of the new lanthanide hydroxynitrate phases. Both Yb-2(OH)(5)NO3 center dot 2H(2)O and Yb-2(OH)(5)NO3 center dot H2O adopt orthorhombic structures in which the nitrate anion is coordinated to the Yb3+ cations within the hydroxide layer and are largely resistant to anion exchange. This is in contrast to the Ln(2)(OH)(5)NO3 center dot 1.5H(2)O phases, which undergo facile anion exchange reactions at room temperature, indicating that the nitrate resides in the interlayer gallery At temperatures above 200 degrees C, the three layered phases were determined to be intermediates in the synthesis of Yb4O(OH)(9)NO3 (4), which has a framework structure with the uncoordinated nitrate anions located in one-dimensional channels The in situ diffraction technique has allowed for a detailed kinetic and mechanistic investigation of the synthesis and revealed that the layered ytterbium hydroxynitrate phases form via a two-dimensional phase boundary-controlled growth mechanism It was also possible to estimate the activation energies for the hydrothermal synthesis of Yb-2(OH)(5)NO3 center dot H2O and Yb-2(OH)(5)NO3 center dot 2H(2)O from basic solution, as +29 and +67 kJ/mol, respectively