Search

The syntheses and systematic X-ray investigations of complexes [Cp.sub.2]Nb(SiY[Me.sub.2])(H)(SiX[Me.sub.2]) and the neutron diffraction (ND) studies of complexes [Cp.sub.2]Nb-(SiH[Me.sub.2](H)(SiCl[Me.sub.2]) and [Cp.sub.2]Nb(SiH[Me.sub.2])(H)(SiBr[Me.sub.2]) is reported. The complexes show the largest structural distortions for the silyl groups substituted by heavy halogen atoms.

The syntheses of the uranium complexes (U(N(SiMe3)2)2(N(SiMe3)(SiMe2ch2b(C6F5)3))) and (U(C(Ph)(NSiMe3)2)2(mu3-BH4)2) are presented. Results demonstrate that the X-ray diffraction has the ability to unveil hydrogen positions unequivocally in uranium-containing compounds if some basic criteria are met. The comparison of the X-ray and neutron structure of the compound (U(N(SiMe3)2)2(N(SiMe3)(SiMe2ch2b(C6F5)3))) and the X-ray structure of the compound (U(C(Ph)(NSiMe3)2)2(mu3-BH4)2) are described.

The essential role of neutron diffraction in the full and precise geometrical characterization of large hydrido metal clusters is demonstrated. This study of [H4Co4(C5Me4Et)4], is the first compound H4Co4 compound that has been fully characterized by the neutron diffraction technique.

Deuterium labeling is a powerful way to gain mechanistic information in biology and chemistry. However, selectivity is hard to control experimentally, and labeled sites can be difficult to assign both in solution and in the solid state. Here we show that very selective high-deuterium contents can be achieved for the polyhydride ruthenium phosphine complex [RuH2(H2)2 (PCyp3)2] (1) (PCyp3 = P(C3H9)3). The selectivity of the H/D exchange process is demonstrated by multinuclear NMR and neutron diifraction analyses. It has also been investigated through density functional theory (DFT) calculations. The reactions are performed under mild conditions at room temperature, and the extent of deuterium incorporation, involving selective C--H bond activation within the cyclopentyl rings of the phosphine ligands, can easily be tuned (solvent effects, D2 pressure). It is shown that D2 gas can inhibit the C--H/C--D exchange process. [ABSTRACT FROM AUTHOR]

A single-crystal neutron diffraction analysis of the cluster complex [H(4)Co(4)(C(5)Me(4)Et)(4)] was carried out on the new quasi-Laue diffractometer VIVALDI at the Institut Laue-Langevin. The structure consists of four face-bridging hydrides attached to a tetrahedral cobalt metal core. Average distances and angles in the core of the molecule are as follows: Co-Co = 2.571(8), Co-C = 2.158(6), Co-H = 1.749(7), H.H = 2.366(9) A; Co-H-Co = 94.6(3), H-Co-H = 85.1(3) degrees. The hydride ligands are located off the Co-Co-Co planes by an average distance of 0.923(8) A. It is suggested that the dimensions of the HCo(3) fragments found in this molecule provide reasonable estimates for analogous distances and angles associated with chemisorbed H atoms situated on the 3-fold hollows of a cobalt surface. Crystallographic details: space group P2(1)/a (monoclinic); a = 21.979(2), b = 10.924(1), c = 34.406(2) A; beta = 90.81(1) degrees; Z = 8. Final agreement factor: R(F) = 0.099 for 3779 reflections [I > 2sigma(I)] collected at 20 K.