Crystal and molecular structures of [AsPh4][Ln{S2P(OEt)2}4](Ln = La or Er) and their comparison with results obtained in solution from paramagnetic nuclear magnetic resonance data

Abstract

The crystal structures of the title compounds have been determined from diffractometer data. The crystals of both compounds are monoclinic, space group P2₁/c, and have four molecules in unit cells of dimensions: Ln = La, a= 20.053(7), b= 15.207(3), c= 20.389(4)Å, β= 112.02(2)°(R= 0.071); Ln = Er, a= 19.972(3), b= 15.148(2), c= 20.244(3)Å, β= 112.27(1)°(R= 0.059). In both cases the lanthanide ion is co-ordinated to eight sulphur atoms, the average Ln–S distances being 2.989 (La) and 2.858 Å(Er). The co-ordination polyhedra are both almost perfect D_2d dodecahedra (mmmm isomer). Although the compounds have similar structures in the solid state, in solution they are quite different as demonstrated by paramagnetic n.m.r. data. The change in the observed ³¹P dipolar shift is shown to be in accord with a change from dodecahedral to square antiprismatic geometry for such compounds when Ln = holmium.