MODEL OF SHORT-RANGE ORDER IN A CONCENTRATED LACL3 AQUEOUS-SOLUTION FROM X-RAY-DIFFRACTION STUDIES

A concentrated aqueous solution of LaCl3 has been investigated by the X-ray diffraction method. The main features of the pair function are c onsistent with the presence of the [La(H2O)9Cl2]+ complex additionally hydrated in the second sphere. The outer-sphere Cl- ions are hydrogen bonded to the inner-sphere water molecules. The La3+-Cl- distance poi nts either to a trigonal orientation of inner-sphere water molecules a nd the hydrogen bond angle of 170-degrees or to the tilt angle of 30-d egrees and a linear hydrogen bond.