Search

The reactions of europium and ytterbium with 2,6-di-tert-butylphenol were studied by the metal vapour synthesis technique and by dissolution in liquid ammonia. The lanthanide complexes [Eu(OC6H3But2-2,6)2(THF)3]·0.75C7H8 1 and [Yb(OC6H3But2-2,6)2(NCMe)4] 2 were synthesized and characterized by X-ray diffraction studies.

Europium(II) hydrotris(pyrazol-1-yl)borate complexes, Eu(HBpz3)2L2 (L=diphenylsulfoxide (1) and bis(pentamethylene)urea (2)), have been synthesized. Characterization of 1 and 2 by infrared absorption spectroscopy points to coordination of the neutral ligands through the sulfoxide and carbonyl oxygens, respectively. This was corroborated by X-ray diffraction analysis. In both compounds the metal centre is eight-coordinate by way of the six nitrogens of the two tridentate pyrazolyl ligands and the oxygen atoms of the diphenylsulfoxide or bis(pentamethylene) urea ligands, in a square antiprismatic configuration. Both complexes are luminescent at 77 K and display emission bands with maxima at 610 and 632 nm for 1 and 2, respectively.

Tetra(tetraphenylimidophosphinato)thorium, Th(tpip)4 (1), was obtained from Th(NO3)4·4H2O and Ktpip in aqueous medium. The analogous uranium compound, U(tpip)4 (2), has been prepared by reacting UCl4 with Ktpip in a 1:4 stoichiometric ratio, either in THF or in aqueous solution. X-ray diffraction analysis showed that compounds 1 and 2 were isostructural. The metal center is eight-coordinate by way of four bidentate tetraphenylimidophosphinate ligands in a square antiprismatic configuration. UCl(tpip)3 (3) has been isolated from the reaction of uranium tetrachloride with 3 equiv. of Ktpip in aqueous solution. When this reaction was run in THF both compounds, U(tpip)4 and UCl(tpip)3, were obtained. The molecular structure of 3 has been determined by X-ray crystallography. The uranium atom is seven-coordinate in a pentagonal bipyramidal configuration. These compounds were also characterized by infrared and 1H and 31P NMR spectroscopies.

The complexes Th(HBPz3)2XnCl2−n (where Pz = pyrazolyl, X = OPri, OBut, OPh, OPh-2,3,5-Me3, OPh-2,4,6-Me3 for n = 1 or 2 and X = CH2SiMe3, SBut for n = 2) have been prepared by reaction of Th(HBPz3)2Cl2 with the appropriate MX reagent (M = Na or Li for X = CH2SiMe3) and were characterized by C, H, N elemental analysis, IR and 1H NMR spectroscopies and in the case of Th(HBPz3)2(OPh)2, by single crystal X-ray diffraction. The coordination polyhedron around the thorium is square antiprismatic, distorted towards dodecahedral. Variable temperature 1H NMR studies of the complexes in solution revealed that they are fluxional, probably due to a facile interconversion of the common eight-coordinate polyhedra; these 1H NMR studies also showed hindered rotation of the bulky OPh-2,4,6-Me3 groups in the complexes containing these ligands.

A steric coordination number of a ligand is defined, based on the solid angle comprising the van der Waals' spheres of the atoms of that ligand, as an alternative to the formal coordination number in discussing structural aspects of lanthanide and actinide coordination and organometallic compounds. The study of the bond lengths in 274 structurally characterized compounds of the lanthanides (including Sc and Y), in oxidation states II and III, and the actinides (Th and U), in oxidation states III and IV, was the basis to derive ligand effective radii which are discussed in relation to bonding, coordination geometries, metal ionic radii and oxidation states. Potential uses of the new definition of coordination number and of the ligand effective radii obtained in molecular structure comparison and bond length prediction are also discussed.