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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.

X-ray and neutron diffraction are used to examine the single crystals of [h.sub.8]-naphthalene over a wide range of temperatures and the anisotropic displacement parameters (ADPs) of carbons and hydrogens are measured. A considerable reduction is seen in the ratio of number of adjustable parameters/numbers of independent observations by applying the treatment to multi-temperate diffraction data.

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 novel disilazane compound 2-pyridinetetramethyldisilazane is prepared. The competition between N-pyridine coordination and Si-H bond activation is studied through its reactivity with two ruthenium complexes.

A single-crystal neutron diffraction study of one of the yttrium cluster complexes is presented. The results have demonstrated the existence of a 4-coordinate hydrogen atom in a discrete molecular species.

Four isomorphous complexes of formula [M(L)4(H2O)2]SO4.2H2O (M=Co, Ni, Cu, Zn) is isolated and characterized by single-crystal X-ray diffraction and neutron diffraction. The system undergoes a disorder-order transition on slow cooing that provides insight into the nature of communication between water squares.

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.

Phenol.nitroxide radicals were studied using neutron diffraction, as a model for hydrogen atom abstraction by peroxyl radicals.

Hsub20ssub6(CO)sub18 is an example of a non-octahedral hexanuclear cluster and was first prepared from the vacuum pyrolysis of Ossub3(CO)sub12 in 1976. A single-crystal neutron structure determination of Hsub2Ossub6(CO)sub18 is now reported, including two hydrogen atoms not previously found in original X-ray studies. The factors resulting in the filling of interstitial sites by hydrogen are still not fully understood, and it is not automatic that a H atom will fill a cavity.