Eight-co-ordination in lanthanide pyrazolylborate chemistry: Crystal structures of [LaTp(2)(Me,Me)(MeCN)(O3SCF3)]center dot MeCN,[NdTp(2)(Me,Me)(MeCN)(2)][O3SCF3] and [LaTp(2)(Me,Me)(NO3)]center dot MeCN[Tp(Me,Me) equals tris(3,5-dimethylpyrazolyl)hydroborate]

The reaction of [LnTp(2)(Me,Me)][O3SCF3][Ln = La, Ce, Pr or Nd; Tp(Me,Me) = tris(3,5-dimethylpyrazolyl)hydroborate] in toluene with acetonitrile gave complexes of stoichiometry LnTp(2)(Me,Me)(MeCN)(2)(O3SCF3) (Ln = La, Ce, Pr or Nd). The structures of those of La and Nd have been determined by X-ray crystallography and found to be ionization isomers of each other: [LaTp(2)(Me,Me)(MeCN)(O3SCF3)]. MeCN consists of neutral molecules while [NdTp(2-)(Me,Me)(MeCN)(2)][O3SCF3] adopts an ionic structure. The structure of [LaTp(2)(Me,Me)(NO3)] has been determined for comparison. The co-ordination environment of the metal centres in all three complexes was shown by polytopal analysis to be dodecahedral in contrast to that (square antiprismatic) commonly adopted by complexes involving unsubstituted hydrotris(pyrazolyl)borate.