Alison J. Edwards

Reduction of a range of amido- and aryloxy-aluminum dihydride complexes, e.g. [AlH2(NR3){N(SiMe3)2}] (NR3 = NMe3 or N-methylpiperidine (NMP)), with -diketiminato dimagnesium(I) reagents, [{(ArNacnac)Mg}2] (ArNacnac = [HC(MeCNAr)2]-, Ar = mesityl (Mes) or 2,6-xylyl (Xyl)), have afforded deep red mixed valence aluminum hydride cluster compounds, [Al6H8(NR3)2{Mg(ArNacnac)}4], which have an average Al oxidation state of +0.66, the lowest for any well-defined aluminum hydride compound. In the solid-state, the clusters are shown to have distorted octahedral Al6 cores, having zero-valent Al axial sites and mono-valent AlH2- equatorial units. Several novel by-products were isolated from the reactions that gave the clusters, including the Mg‒Al bonded magnesio-aluminate complexes, [(ArNacnac)(Me3N)Mg‒Al(-H)3[{Mg(ArNacnac)}2(-H)]]. Computational analyses of one aluminum hydride cluster revealed its Al6 core to be electronically delocalized, and to possess one unoccupied, and six occupied, skeletal molecular orbitals.

Determining the structures of nanoparticles at atomic resolution is vital to understand their structure–property correlations. Large metal nanoparticles with core diameter beyond 2 nm have, to date, eluded characterization by single-crystal X-ray analysis. Here we report the chemical syntheses and structures of two giant thiolated Ag nanoparticles containing 136 and 374 Ag atoms (that is, up to 3 nm core diameter). As the largest thiolated metal nanoparticles crystallographically determined so far, these Ag nanoparticles enter the truly metallic regime with the emergence of surface plasmon resonance. As miniatures of fivefold twinned nanostructures, these structures demonstrate a subtle distortion within fivefold twinned nanostructures of face-centred cubic metals. The Ag nanoparticles reported in this work serve as excellent models to understand the detailed structure distortion within twinned metal nanostructures and also how silver nanoparticles can span from the molecular to the metallic regime.

The PSiP pincer-supported complex (^CyPSiP)PdH [^CyPSiP = Si(Me)(2-PCy₂-C₆H₄)₂] has been implicated as a crucial intermediate in carboxylation of both allenes and boranes. At this stage, however, there is uncertainty regarding the exact structure of (^CyPSiP)PdH, especially in solution. Previously, both a Pd(II) structure with a terminal Pd hydride and a Pd(0) structure featuring an η²-silane have been proposed. In this contribution, a range of techniques were used to establish that (^CyPSiP)PdH and the related Pt species, (^CyPSiP)PtH, are true M(II) hydrides in both the solid state and solution. The single-crystal X-ray structures of (^CyPSiP)MH (M = Pd and Pt) and the related species (^iPrPSiP)PdH [^iPrPSiP = Si(Me)(2-PⁱPr₂-C₆H₄)₂] are in agreement with the presence of a terminal metal hydride, and the exact geometry of (^CyPSiP)PtH was confirmed using neutron diffraction. The ¹H and ²⁹Si{¹H}NMR chemical shifts of (^CyPSiP)MH (M = Pd and Pt) are consistent with a structure containing a terminal hydride, especially when compared to the chemical shifts of related pincer-supported complexes. In fact, in this work, two general trends relating to the ¹H NMR chemical shifts of group 10 pincer-supported terminal hydrides were elucidated: (i) the hydride shift moves downfield from Ni to Pd to Pt and (ii) the hydride shift moves downfield with more trans-influencing pincer central donors. DFT calculations indicate that structures containing a M(II) hydride are lower in energy than the corresponding η²-silane isomers. Furthermore, the calculated NMR chemical shifts of the M(II) hydrides using a relativistic four-component methodology incorporating all significant scalar and spin–orbit corrections are consistent with those observed experimentally. Finally, in situ X-ray absorption spectroscopy (XAS) was used to provide further support that (^CyPSiP)MH exist as M(II) hydrides in solution.