The [Ln(H20)9](CF3SO3) 3 complexes with Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Yb and Lu form an isomorphous series of hexagonal structures, a= 13.990(6)-13.259(2), c= 7.444(2)-7.751 (1)A, P63/m, Z = 2. Full crystal data have been published [Harrowfield, Kepert, Patrick & White (1983). Aust. J. Chem. 36,[483][484][485][486][487][488][489][490][491][492]. The [Ln(H20)9] 3+ moiety has a tricapped trigonal prism geometry. The consequences of the lanthanoid contraction were determined from structure refinements with X-ray diffraction intensity data measured for a charge density study at 295 K (wR=0.022-0.051). The Nd structure was also refined with neutron diffraction data (wR = 0.042). The lanthanoid contraction for the bonds to the equatorial oxygens is less than it is for the prism oxygens. This is associated with weakening of the hydrogen-bond network for the equatorial water, while that of the prism water is strengthened. This reflects a change in the interaction between the metal and the ligating water molecules resulting from their orientation. At the upper end of the 4fseries, the trigonally oriented water is less strongly bound.

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An accurate set of X-ray data collected at 298 K was used to refine the structure and study the deformation density of the title compound for 5007 reflections. A neutron structure confirmed the accuracy of bond lengths reported in an earlier determination. The radial structure of the deformation density near the Cu atom also varies, in a manner correlated with metal-oxygen bond length, and consistent with trends in the isomorphous magnesium and nickel structures. Large differences in bond lengths affected by Jahn-Teller distortion are influenced by interactions with neighbouring groups. The strengths of the metal-oxygen bonds are increased by hydrogen bonding of the ligating water molecules, and decreased by interaction between the oxygen lone pairs and the ammonium group.

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