X-RAY AND MULTINUCLEAR MAGNETIC-RESONANCE STUDY OF THE COMPLEXES OF LANTHANUM(III) WITH 2,2'/6',2''-TERPYRIDINE

The reaction between La(NO3)(3) . 6H(2)O and 2,2':6',2 ''-terpyridine (terpy) in acetonitrile solution was investigated by H-1, O-17, and La-139 NMR spectroscopy. The crystal structure of [La(NO3)(2)(terpy)(2)] [La(NO3)(4)(terpy)]. CH3CN .(1)/2H2O was determined by X-ray diffraction: triclinic; space group P ($) over bar 1; a = 14.979(4) Angstrom, b = 17.501(10) Angstrom, c = 11.603(5) Angstrom; Z = 2; alpha = 106.34(4)degrees, beta = 94.22(3)degrees, gamma = 83.30(3)degrees. At convergence, R(F) = 0.053 and R(W) = 0.032 for 4012 reflections. In solution, the La-139 NMR coordination shell. O-17 NMR spectroscopy indicates that during the complexation by terpy, coordinated water is totally displaced from the coordination sphere whereas the nitrate groups remain partially bound. Proton NMR data confirm the total displacement of water and show that two terpy molecules are in close proximity when they are coordinated to the same La(III) ion. From the NMR results, it is shown that during the complexation process seven different La(III) species can be observed: [La(NO3)(3)(CH3CN)(4)], [La(NO3)(3)(CH3CN)(3)(H2O)], [La(NO3)(3)(terpy)(CH3CN)], [La(NO3)(3)(terpy)(H2O)], [La(NO3)(4)(terpy)(CH3CN)](-),[La(NO3)(4)(terpy)(H2O)](-), and [La(NO3)(2)(terpy)(2)](+). The structure of the cationic complex in solution shows similarities with the solid state compound, but the anionic complex is affected by solvation. Comparisons are made with the La(III) complexes previously obtained with 1,10-phenanthroline and 2,2'-bipyridine as well as with data reported in the literature.