JOURNAL OF SOLID STATE CHEMISTRY 139, 259 — 265 (1998) ARTICLE NO. SC987838 Crystalline and Molecular Structures of Anhydrous Lanthanide Perchlorates Ln(ClO 4 ) 3 with Ln  La, Ce, Pr, Sm, Eu, Ho, Er, Tm, and Lu J. L. Pascal, F. Favier, and F. Cunin Laboratoire des Agre ´ gats Mole ´ culaires et Mate ´ riaux Inorganiques (UPRESA 5072 CNRS), Universite ´ Montpellier II, Place E. Bataillon, C.C.015, F-34095 Montpellier Ce ´ dex 5, France and A. Fitch and G. Vaughan European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex, France Received December 4, 1997; in revised form March 20, 1998; accepted April 5, 1998 The anhydrous perchlorates Ln(ClO 4 ) 3 , where ClO 4 is coor- dinated to Ln atoms (Ln  La, Ce, Pr, Sm, Eu, Ho, Er, Tm, and Lu) crystallize in two distinct groups of isostructural species. Rietveld refinements show that from lanthanum to thulium (low temperature form), the crystal system is hexagonal (space group P6 3 /m, Z  2) with 9.400(3) A  < a < 9.201(1) A  and 5.918(1) A  < c < 5.563(1) A  . The Rietveld refinement converged to R F  0.033, R p  0.029, and R wp  0.053 for Eu(ClO 4 ) 3 . The channeled structure is built on the basis of slightly distorted tricaped trig- onal Eu centered prisms of nine oxygen atoms belonging to nine tridentate [ClO  ]. Thullium (high temperature form) and lutetium crystallize in trigonal R3c unit cells (Z  6) with, respectively, a  8.13286(2) A  , c  24.1586(1) A  , and a  8.11559(4) A  , c  24.0047(1) A  . For Lu(ClO 4 ) 3 , R F , R p , and R wp were 0.039, 0.046, and 0.061, respectively. Its molecular structure consists of infinite layers of Lu atoms in a tricaped trigonal antiprism surrounding of oxygens. Layers and linkages between layers are ensured by simultaneously bridging and chelating tridentate [ClO 4 ].  1998 Academic Press INTRODUCTION In the development of new preparative methods for metal oxides as dispersed powders, the thermolysis at moderate temperatures of a fully inorganic precursor with weak oxy- ligands should be an alternate method of synthesis which can promote attractive properties (1). For example, nitrates are compounds of choice for this method in the preparation of ceramics (2). The possibilities of varying the conditions of pressure, the heating rate, and the nature of the gaseous  To whom correspondence should be addressed. E-mail: pasfav@crit. univ-montp2.fr. environment add further to the richness of the process. Perchlorates generally decompose below 250—300°C, giving fine powders of oxides in which the metal is in its highest oxidation state. However, starting from lanthanide per- chlorates and with the exception of Ce(ClO  )  , the resulting powders are oxychlorides rather than oxides. In order to control the structure and morphology of the resulting ma- terial, it nevertheless remains of importance to know the structure of the precursor as well as those of the successive intermediate solids. In previous papers (3, 4) we described the synthesis of a series of anhydrous rare earth perchlor- ates, M(ClO  )  with M"Y, La, Pr, Nd, Sm, Gd, and Er, and we proposed tentative structural assignments essential- ly based on infrared and Raman data, since perchlorates are obtained as microcrystalline powders rather than single crystals. Although X-ray powder diffraction techniques have significantly improved (5) over the past 10 years and are now used to solve the structures of ever more complex species (6), determination of the structure of anhydrous perchlorates by powder diffraction has never been reported. We have recently had the opportunity to be among the first users of the new beam line 16 at the European Synchrotron Radiation Facility (ESRF), which is devoted to X-ray pow- der diffraction. Recording data on this line has allowed us to determine the crystalline and molecular structures of a series of ¸n(ClO  )  compounds with ¸n"La, Ce, Pr, Sm, Eu, Ho, Er, Tm, and Lu. EXPERIMENTAL Synthesis Caution : Chlorine trioxide and perchlorates are highly reactive compounds particularly on contact with organic 259 0022-4596/98 $25.00 Copyright  1998 by Academic Press All rights of reproduction in any form reserved.