Thermal behavior of two novel Ho(III) dicarboxylates

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

Campinas, Brasil

Workshop; Latin American Workshop on Applications of Powder Diffraction; 2007

LNLS

ing of lanthanide dicarboxylates as building blocks are currently focus of atten-tion for materials engineering. The structure and properties of these materials aresensitively conditioned by the functionality of the organic and inorganic struc-tural agents. Such molecular-based materials exhibit potential utilities in severalareas, i.e. their application as "templates" or as precursors in decomposition pro-cesses (thermal o chemical) in ceramic synthesis. The design of the synthesis ofthese solids, namely pressure and temperature conditions, is also a key factor thatallows to expand the variety of structural types and consequently, their dimen-sionality and functionality. Hydrothermal conditions are more suitable for prepar-ing 3D solids with extended MOM networks, which favor better thermal stabil-ity, since they enhance metalligand interactions rather than metalwater coordi-nation. 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 hydrothermalconditions, respectively, and their morphology was observed by SEM. The thermalbehavior (TGA, DSC, TDRX) and spectroscopic (FTIR) and magnetic (AC suscep-tibility) properties were analyzed in connection to the structural features revealedby single-crystal X-ray di®raction. It is worth mentioning that thermal degrada-tion shows interesting transitions whose study is essential to estimate the potentialability of these materials at different work temperatures. The analysis of the resultsshowed that the removal of hydration water molecules in I leads to an amorphousphase that recrystallizes in the space group P2/m with the cell parameters: a =19.378(5), b = 8.157 (4), c = 4.236(1) A, and beta= 92.22(1). On further heating thisphase remains stable, with increasing crystallinity, up to succinate ion decomposi-tion. Compound II essentially retains its crystalline structure when the first watermolecule is lost, the decrease in the XRPD lines intensity being the most outstand-ing dfference between patterns corresponding to different temperature treatments.Acknowledgements: The authors thank to CONICET: PID 4929 and PIP 6007, AN-PCyT:PICT 03041, CICPBA, UNLP and UNSL Rep¶ublica Argentina, and CSIC, Spain,for ¯nancial support; Dr. A. P. Ayala for his assistance in measuring the Raman spec-tra. G. P., G. E. E. and G. E. N. are members of the CONICET. C.G.P. and M.C.B.acknowledges a  a CONICET fellowship