FT-IR and fluorometric investigation of rare-earth and metal ion solvation .16. Solid state and solution study of acetonitrile-coordinated lanthanide solvates [Ln(CH3CN)(9)](AlCl4)(3)

The CH3CN coordinated lanthanide solvates [Ln(CX(3)CN)(9)](AlCl4)(3) have been studied by means of luminescence (X = H, D; Ln = Eu, Tb) and FT-IR spectroscopy (X = H; Ln = La, Nd, Gd, Er, Lu). High resolution luminescence spectra, recorded at 77 K, of the [Eu(CH3CN)(9)](AlCl4)(3) microcrystalline compound, show the Eu-III ion located in one unique coordination site with a local symmetry close to D-3h. The same local structure is preserved in Eu-doped La and Gd solvates, pointing to an isostructural series of compounds. The lifetime of the Eu(D-5(0)) level amounts to 5.07 ms in the deuterated solvate. The tricapped trigonal prismatic geometry is lost in 0.01 M solutions in anhydrous acetonitrile and propylene carbonate. Analysis of the D-5(0) <-- F-7(0) transition points to the presence of at least two different species in equilibrium. Vibrational spectra evidence a sizable Ln-acetonitrile interaction substantiated by the shifts of the nu(2) and nu(3) + nu(4) vibrations which increase linearly with the increase in electronic density of the lanthanide ions and which are identical to those observed for lanthanide perchlorate and nitrate solutions under the same experimental conditions. This means that the Ln-acetonitrile interaction is mainly governed by electrostatic factors. In mixed propylene carbonate-acetonitrile solutions of [La(CH3CN)(9)](AlCl4)(3) complexes, lanthanum ions are preferentially solvated by propylene carbonate molecules for R = [CH3CN](t)/[Ln(III)](t) less than or equal to 50. For R = 100, four acetonitrile molecules are bonded to the lanthanum ion.