Thermal behavior of two novel Ho(III) dicarboxilates

BERNINI, M. C.; BRUSAU, E. V.; NARDA, G. E.; POZZI, G.; ECHEVERRÍA, G.; PUNTE, G.

Campinas Brasil

Congreso; Latin American Workshop on Powder Diffraction; 2007

Laboratório Nacional de Luz Síncrotron (LNLS)

Studies on hybrid organic/inorganic coordination polymers with networks consisting of lanthanide dicarboxylates as building blocks are currently focus of attention for materials engineering. The structure and properties of these materials are sensitively conditioned by the functionality of the organic and inorganic structural agents. Such molecular-based materials exhibit potential utilities in several areas, i.e. their application as "templates" or as precursors in decomposition processes (thermal o chemical) in ceramic synthesis. The design of the synthesis of these solids, namely pressure and temperature conditions, is also a key factor that allows to expand the variety of structural types and consequently, their dimensionality and functionality. Hydrothermal conditions are more suitable for preparing 3D solids with extended M–O–M networks, which favor better thermal stability, since they enhance metal–ligand interactions rather than metal–water coordination. Two novel dicarboxylates formulated as [Ho2(C4H4O4)3(H2O)4].6H2O (I) and [Ho2(C4H4O4)3(H2O) 2].H2O (II) were obtained under mild and hydrothermal conditions, respectively, and their morphology was observed by SEM. The thermal behavior (TGA, DSC, TDRX) and spectroscopic (FTIR) and magnetic (AC susceptibility) properties were analyzed in connection to the structural features revealed by single-crystal X-ray diffraction. It is worth mentioning that thermal degradation shows interesting transitions whose study is essential to estimate the potential ability of these materials at different work temperatures. The analysis of the results showed that the removal of hydration water molecules in I leads to an amorphous phase that recrystallizes in the space group P2/m with the cell parameters: a = 19.378(5), b = 8.157 (4), c = 4.236(1) Å, and b = 92.22(1)º. On further heating this phase remains stable, with increasing crystallinity, up to succinate ion decomposition. Compound II essentially retains its crystalline structure when the first water molecule is lost, the decrease in the XRPD lines intensity being the most outstanding difference between patterns corresponding to different temperature treatments.