Coordination compounds from hydrated lanthanide(III) and yttrium(III) picrates with hexamethylphosphoramide (HMPA)

Coordination compounds were synthesized from ethanolic solution by reaction of hydrated lanthanide (III) and yttrium(III) picrate with hexamethylphosphoramide ligand. Through complexometric titration and microanalytical procedures (C, H, N), the following stoichiometries were proposed: M(pic)3 (HMPA)3 (M=La-Eu, Y), except PM, M (pic)3 (HMPA)2 (M=Eu-Lu). Conductance measurements in nitromethane and acetonitrile indicate the compounds are non-electrolytes, evidencing that picrate anions are coordinated to the metallic centers. The data of infrared absorption spectra permit infer through the oxygen atom. Spectroscopic investigations of the Nd(pic)3. (HMPA)3, and Er(pic)3. (HMPA)2, in the visible region, were made using the hypersensitive 4/9/2 ->4G5/2, 2G7/2 and 4/9/2 ->2H11/2. The optical parameters β, γ and b1/2 were estimated and they are indicative of an electrostatic character of the lanthanide-ligand bond. The emission spectra of the solid Eu(pic)3 (HMPA)3 and Eu(pic)3 (HMPA)2 complexes were interpreted in terms of a D3h symmetry distorted to C3y and C2v, respectively. According to X-Ray powder patterns, six series of diffractograms were obtained: a) Ln(pic)3 (HMPA)3, (Ln=La-Nd); b) Eu(pic)3 (HMPA)2; c) Y(pic)3 (HMPA)2; d) Er (pic)3(HMPA)2; e) Ln (pic)3 (HMPA)2, (Ln=Tb, Dy) and f) Ln (pic)3 (HMPA)2, (Ln=Sm, Gd, Tm, Ho, Yb and Lu). The structures of Nd (pic)3(HMPA)3, Ho(pic)3(HMPA)2 and Y (pic)3(HMPA)2 compounds, were determined by X-ray patterns diffractions of the single crystal. (author)