LIGAND-STABILIZED NICKEL AND PALLADIUM BORIDE COLLOIDS

A route to the first ligand stabilized nickel and palladium boride col loids with core diameters of 1.4 and 1.6 nm is described. The particle s are formed by reaction of the metal complexes Cl2M(PR3)2 (M = Ni, Pd , PR3 = PPr3, PBu3) with B2H6 in toluene at room temperature with 40 - 70% yield. The characterization of the pyrophoric brown powders occur red by elementary analyses, resulting in smallest formula units, which then could be extended to averaged molecular formulas by mass determi nations, using an analytical ultracentrifuge: [Ni6B10Cl1.5(PPr3)]12.5 (1), [Ni6B10Cl1.5(PBU3)]8.5 (2), [Pd4B.5Cl(PPr3)]16.5 (3), and [Pd4B6C l(PBU3)]16.5 (4). From the masses of the colloid cores and their rough ly calculated densities the size of the boride particles could be esti mated. The diameters of 1.6 nm for 1, 3, and 4 are identical within th e experimental error. Only 2 seems to have a slightly reduced diameter of 1.4 nm. 1-4 can be dispersed in inert organic solvents in any conc entration. To confirm these relatively uncertain values high resolutio n transmission electron microscopy has been used. Investigations of 1 and 3 show indeed an averaged particle size of 1.6 +/- 0.3 nm in agree ment with the data derived from the mass determinations. Surprisingly most of the observed particles appear to have amorphous structure. Thi s finding is supported by X-ray powder diffraction experiments, as no significant reflex data could be registered. P-31 and B-11 NMR measure ments have been performed too, however, do not contribute to further c haracterization.