Rare earth thiocyanate complexes with tripiperidinophosphine oxide:: synthesis and characterization.: Crystal structure of Pr(SCN)3(tPPPO)3

The synthesis and characterization of rare-earth (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) thiocyanate adducts with tripiperidinophosphine oxide (tpppO) with general formula (RE)(SCN)(3)(tPPPO)(3) are reported. Conductance measurements in acetonitrile indicate the non-electrolytic nature of the complexes. Infrared absorption spectra evidence that the SCN- ion coordinates through the nitrogen atom (isothiocyanate form) and that tpppO coordinates through the phosphoryl oxygen. X-ray powder patterns suggest the existence of three different crystal forms: (1) La; (2) an isomorphous series including Ce, Nd and Pr,and (3) another isomorphous series, including Sm, Gd, Eu, Ho, Er, Tb, Lu and Y. The visible spectra of the Nd adduct and the calculated parameters beta = 0.98, b(1/2) = 0.072 and delta = 1.06 indicate that the metal-ligand bonds are essentially electrostactic. The emission spectra of the Eu compound showed D-5(0) --> F-7(J) bands (J = 0, 1, 2), suggesting a C,,, symmetry for the coordination polyhedron. The lifetime of the D-5(0) state is 1.28 ms. The emission spectra of the Tb complex presented D-5(4) --> F-7(J) bands (J = 4.5 6) and the Dy complex showed the F-4(9/2) --> H-6(13/2) band. The structure of the Pr complex showed that the coordination polyhedron is a trigonal antiprism, with the isothiocyanate anions in one base and three tpppO ligands in the other. Thermal analyses (TG-DTG) were carried out for the Ce, Nd and Gd adducts. Mass losses start between 250 and 334 degreesC. The final residues at 1300 degreesC are the corresponding phosphates. (C) 2004 Elsevier B.V. All rights reserved.