Total halide abstraction from LnCl3 by Ag[Al(OC(CF3)3)4]/CH3CN has been confirmed for a series of lanthanide metal ions by the structural characterization of [Ln(CH3CN)n][Al(OC(CF3)3)4]3 (n=9, Ln3+=Nd, Eu, Gd, Dy; n=8, Ln3+=Tm) complexes. Evidence for the very low coordinating ability of the [Al(OC(CF3)3)4]- anion towards Ln3+ ions is provided in the solid state (X-ray, IR and Raman spectroscopy) and in anhydrous acetonitrile solution (conductivity, EPR and NMR measurements). In the solid state homoleptic nine-coordinated acetonitrile species are characteristic for lanthanides for the beginning (Nd) and the middle (Eu, Gd, Dy) of the Ln series, with a mono-capped square antiprismatic arrangement of the N donor atoms around the metal centres; while for those from the end of the series (Tm) eight-coordinated species are representative with a square antiprismatic arrangement. In anhydrous acetonitrile solution, conductivity measurements revealed 3:1 electrolyte types for all compounds. EPR and 19F NMR line broadening measurements attest lanthanide complexes free of any coordinating [Al(OC(CF3)3)4]- anion.

Homoleptic acetonitrile complexes [Gd(CH(3)CN)(9)][Al(OC(CF(3))(3))(4)](3) and [Eu(CH(3)CN)(9)][Al(OC(CF(3))(3))(4)](2) have been studied in anhydrous acetonitrile by (14)N- and (1)H NMR relaxation as well as by X- and Q-band EPR. For each compound a combined analysis of all experimental data allowed to get microscopic information on the dynamics in solution. The second order rotational correlation times for [Gd(CH(3)CN)(9)](3+) and [Eu(CH(3)CN)(9)](2+) are 14.5 ± 1.8 ps and 11.8 ± 1.1 ps, respectively. Solvent exchange rate constants determined are (55 ± 15) × 10(6) s(-1) for the trivalent Gd(3+) and (1530 ± 200) × 10(6) s(-1) for the divalent Eu(2+). Surprisingly, for both solvate complexes CH(3)CN exchange is much slower for the less strongly N-binding acetonitrile than for the more strongly coordinated O-binding H(2)O. It is concluded that this exceptional behavior is due to the extremely fast water exchange, whereas the exchange behavior of CH(3)CN is more regular. Electron spin relaxation on the isoelectronic ions is much slower than on the O-binding water analogues. This allowed a precise determination of the hyperfine coupling constants for each of the two stable isotopes of Gd(3+) and Eu(2+) having a nuclear spin.

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Homoleptic acetonitrile complexes [Nd(CH3CN)9][Al(OC(CF3)3)4]3, [Dy(CH3CN)9][Al(OC(CF3)3)4]3, and [Tm(CH3CN)8][Al(OC(CF3)3)4]3 have been studied in anhydrous acetonitrile by (14)N and (1)H NMR relaxation. Solvent-exchange rate constants increase from (22 ± 6) × 10(6) s(-1) (Nd(3+)) and (160 ± 40) × 10(6) s(-1) (Dy(3+)) for the nonasolvated ions to (360 ± 40) × 10(6) s(-1) (Tm(3+)) for the octasolvated ions. Electron-spin relaxation of the lanthanide ions studied is similar to that found in aqua ions. This dependence on the binding properties of the coordinating molecules is consistent with the model proposed by Fries et al. for fast electron-spin relaxation of lanthanide ions other than Gd(3+).

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