Assignment of individual structures from intermetalloid nickel gallium cluster ensembles.

Poorly selective mixed-metal cluster synthesis and separation yield reaction solutions of inseparable intermetalloid cluster mixtures, which are often discarded. High-resolution mass spectrometry, however, can provide precise compositional data of such product mixtures. Structure assignments can be achieved by advanced computational screening and consideration of the complete structural space. Here, we experimentally verify structure and composition of a whole cluster ensemble by combining a set of spectroscopic techniques. Our study case are the very similar nickel/gallium clusters of M12, M13 and M14 core composition Ni6+xGa6+y (x + y ≤ 2). The rationalization of structure, bonding and reactivity is built upon the organometallic superatom cluster [Ni6Ga6](Cp*)6 = [Ga6](NiCp*)6 (1; Cp* = C5Me5). The structural conclusions are validated by reactivity tests using carbon monoxide, which selectively binds to Ni sites, whereas (triisopropylsilyl)acetylene selectively binds to Ga sites.

Nanometallurgy in solution: organometallic synthesis of intermetallic Pd-Ga colloids and their activity in semi-hydrogenation catalysis.

Nanoparticles (NPs) of Pd1--xGax (x = 0.67, 0.5, 0.33), stabilized in non-aqueous colloidal solution, were obtained via an organometallic approach under mild conditions using [Pd2(dvds)3] and GaCp* as all-hydrocarbon ligated metal-precursor compounds (dvds = 1,1,3,3-tetramethyl-1,3-divinyl-disiloxane; Cp* = η5-C5Me5; Me = CH3). The reaction of the two precursors involves the formation of a library of molecular clusters [PdnGamCp*y(dvds)z], as shown by liquid injection field desorption ionization mass spectrometry (LIFDI-MS). Full characterization of the catalytic system (HR-TEM, EDX, DLS, PXRD, XPS, NMR, IR, Raman) confirmed the formation of ultra-small, spherical NPs with narrow size distributions ranging from 1.2 ± 0.2 nm to 2.1 ± 0.4 nm (depending on the Pd : Ga ratio). The catalytic performance of the Pd1--xGax NPs in the semi-hydrogenation of terminal and internal alkynes and the influence of the gallium content on product selectivity were investigated. The highest activities (65%) and selectivities (81%) are achieved using colloids with a "stoichiometric" Pd/Ga ratio of 1 : 1 at 0 °C and 2.0 bar H2 pressure. While lower Ga ratios lead to an increase in activity, higher Ga contents increase the olefin selectivity but are detrimental to the activity.