Hydration water and crystal structure in Lanthanide malonates

ECHEVERRÍA, G.; PUNTE, G.; BRUSAU, E. V.; PEDREGOSA, J.C.; NARDA, G. E.

Villa Giardino, Córdoba

Congreso; IX Seminario Latinoamericano de Análisis por Técnicas de Rayos X; 2004

 [Ln2(CO2(CH2)CO2)(H2O)6]·2H2O, where Ln= Eu or Nd, were investigated by x ray single crystal diffraction at 120 and 290K. The results showed that they are isoestructural and crystallize in the orthorhombic system. The  independent  Ln  cations coordination polyhedra consist of nine oxygen atoms belonging to four malonate ions and three coordination waters. The malonate anions are arrange forming different chains which build the three dimensional structure. These chains disposition favors the formation of channels where hydration waters are located forming hydrogen bonds. No structural change is observed within the studied temperatures. These results are compared with those obtained from a reported hydrate of Nd malonate, Nd2(CO2(CH2)CO2)(H2O)6, which crystallizes in the monoclinic system and presents a phase transition in the range 236 - 293 K. The comparison of the different hydrates allows to discuss the influence of hydration waters on the crystal structure and on the phase stabilization at temperatures below ambient.