Crystal and molecular structures of [AsPh4][Ln(S2PMe2)4](Ln = Ce or Tm) and their comparison with results obtained from paramagnetic nuclear magnetic resonance data in solution

Abstract

The crystal structures of the title compounds have been determined from diffractometer data. The crystals of the cerium compound are tetragonal, space group P4₂22 with four molecules in the unit cell of dimensions a= 11.461(2), c= 33.479(6)Å(R= 0.060). The thulium analogue is orthorhombic, space group Pca2₁ with four molecules in the unit cell of dimensions a= 19.899(3), b= 11.451(2), c= 19.051(2)Å(R= 0.037). In both compounds the lanthanide ion is co-ordinated to eight sulphur atoms with average Ln–S distances of 2.991 Å(Ce) and 2.870 Å(Tm). The co-ordination polyhedra are D_2d, dodecahedra (mmmm isomer) distorted towards the D₂ square antiprism, the cerium compound having two independent molecules in the unit cell, both with 222 crystallographic symmetry. Despite the difference in crystallography between the Ce and Tm compounds, the molecular structures are quite similar in the solid state. However, in solution this is not the case as shown by paramagnetic n.m.r. data. The ³¹P dipolar shifts are shown to be in accord with a change from dodecahedral to square-antiprismatic geometry when Ln = Dy.