Anionic tris(cyclopentadienyl)actinide(IV) complexes

Abstract

Anionic complex salts, A⁺[M(cp)₃(NCS)₂]^–(cp =η-C₅H₅), where A =[K(Crypt)](Crypt = Cryptofix-222) or NMe₄ and M = U, and A = AsPh₄ with M = U, Np, or Pu, have been prepared. Spectrophotometric and other evidence indicates trigonal-bipyramidal co- ordination for the metal atoms in the uranium complex anions, as in the known structure of the neutral complex [U(cp)₃(NCS)(NCMe)]. The η-methylcyclopentadienyl analogue of the last complex is more difficult to obtain and dissociates more readily than the cp compound. Although evidence for the formation of uncharged [Np(cp)₃(NCS)(NCMe)] in solution was obtained, the neutral neptunium complex could not be isolated and [Pu(cp)₃(NCS)] reacts even less readily with methyl cyanide. A systematic investigation of the effects of the additional anion Y^– in various solvents for the systems [U(cp)₃XY]^–, where X and/or Y = F^–, OH^–, CN^–, NCBH₃^–, NCS^–, and NCO^–, shows that, in addition to steric factors, the specific distribution of the excess negative charge plays an important role. The first mixed anionic complex K[U(cp)₃(OCN)(NCS)] was also obtained. Infrared, ¹H n.m.r. (U compounds only), and near-i.r.–visible spectra are reported.