THE CRYSTAL AND MOLECULAR STRUCTURE OF GADOLINIUM 3,5-DINITROBENZOATE TRIHYDRATE. D. Ülkü, M.N. Tahir, C. Ünaleroglu, Physics Department, Hacettepe University, Ankara, Turkey

In the crystal structure of the title molecule, Gd ( C₇H₃N₂O₆)₃.3H₂, Gd ions are bridged by the carboxylate groups to form linear polymeric chains. The coordination around Gd is eight fold; six O atoms from six carboxylate groups and two from water molecules. The third water molecule in the formula unit is crystal water. The structural studies of rare earth carboxylates except Cerium 3,5 -dinitrobenzoate dihydrate has shown that the carboxylate groups may be cooordinated simultaneously in three modes: chelating, bridging and chelating-bridging. The structure of Gd-compound has only bridging type of bonding as observed in the Ce-compound. The bridges between the consecutive Gd-atoms involve four ligands on one side and two on the other; causing a nonequidistant and alternating Gd-Gd order within the polymeric chains. Alternating Gd-Gd distances are 4.255 and 5.061Å respectively. The average GdO distances for carboxylate oxygens is 2.375Å while for water oxygens the same distance has an average value of 2.500Å. Crystals are triclinic, space group P1, with a=9.274, b= 11.483, c= 13.745Å, [[alpha]]= 107.11deg., ß=90.50deg., [[gamma]]=93.82deg. and Z=2. Data collection CAD4, structure solution MolEN software package.