Search

The bimetallic M20 and M21 compounds, {[Cu3Ag17{S2P(OiPr)2}12]0.5 [Cu4Ag16{S2P(OiPr)2}12]0.5} ({[1a]0.5[1b]0.5}) and [Cu4Ag17{S2P(OiPr)2}12](PF6) (2), have been structurally characterized, in which the Cu(I) ions are randomly distributed on the eight outer positions capping the eight-electron [Ag13]5+ core. DFT calculations show that the statistical disorder results from the nearly neutral preference of copper to occupy any of the eight outer positions. Surprisingly, the UV–Vis absorption spectra of the M20 and M21 bimetallic nanoclusters display an almost identical absorption profile as that of their homometallic [Ag20{S2P(OiPr)2}12] and [Ag21{S2P(OiPr)2}12]+ relatives. This is rationalized by TD-DFT calculations, which show that the frontier orbitals of such eight-electron alloys are largely independent from the nature of the capping metal ions. A blue-shifted absorption is observed upon replacing by Au the central Ag atom in 2, forming the trimetallic compound [Cu4AuAg16{S2P(OiPr)2}12](PF6) (3). [ABSTRACT FROM AUTHOR]

DFT calculations were carried out on a series of tetrahedral 16-atom superatomic clusters having 20 or 18 jellium electrons (je) and structurally related to Au20, namely, [M16]4−/2− (M = Cu, Ag, and Au) and [M4′M12′′]0/2+ (M′ = Zn, Cd, Hg; M′′ = Cu, Ag, Au). While the bare homonuclear 20-je species required further stabilization to be isolated, their 18-je counterparts exhibited better stability. Lowering the electron count led to structural modification from a compact structure (20-je) to a hollow sphere (18-je). Such a change could be potentially controlled by tuning redox properties. Among the 20-je heteronuclear [M4′M12′′] neutral series, [Zn4Au12] appeared to meet the best stability criteria, but their 18-je relatives [M4′M12′′]+, in particular [Zn4Cu12]2+ and [Cd4Au12]2+, offered better opportunities for obtaining stable species. Such species exhibit the smallest models for the M(111) surface of fcc metals, which expose designing rules towards novel high-dopant-ratio clusters as building blocks of nanostructured materials. [ABSTRACT FROM AUTHOR]

Attempts to expand the versatility of well defined clusters are a relevant issue in the design of building blocks for functional nanostructures. Here, we investigate the plausible formation of related structures from the emblematic highly symmetrical 18‐e [W@Au12] cluster. The calculated [W@Au12Ptn] series, with n = 0, 1, 2, 3, and 4, show cohesion energies, HOMO‐LUMO gap, adiabatic electron affinities (AEAs) and adiabatic ionization potentials (AIPs), indicating a relative stability to the parent cluster [W@Au12] experimentally characterized, where clusters with n = 1 and n = 4 are suggested as the most stable with respect to oxidation. The resulting symmetry lowering away from the high icosahedral symmetry upon adding Pt atoms induces a sizable splitting of the frontiers shells, which in turn effectively modify the properties of the calculated clusters, as observed from calculated optical properties. The estimated absorption spectra show an interesting broadening effect of the absorption peaks, which appears as a useful approach for further design of broad black absorbers, which are able to absorb light in a wider range, with potential capabilities to enhance the efficiency of thin film solar cells and photocatalysis processes, among other applications. Cage doping induces structural modifications along the isoelectronic series given by W@Au12Ptn (n = 0‐4) superatomic clusters, highlight the role of symmetry changes in optical and energetic properties. Such changes are related to interesting broadening effect of the absorption peaks, which can be taken into account in the design of improved broad black‐absorbers. [ABSTRACT FROM AUTHOR]

The isoelectronic doping of dichalcogenolato nanoclusters of the type [Ag 21 {E 2 P(OR) 2 } 12 ] + (E = S, Se) by any heteroatom belonging to groups 9-12 was systematically investigated using DFT calculations. Although they can differ in their global structure, all of these species have the same M@M 12 -centered icosahedral core. In any case, the different structure types are all very close in energy. In all of them, three different alloying sites can be identified (central, icosahedral, peripheral) and calculations allowed the trends in heteroatom site occupation preference across the group 9-12 family to be revealed. These trends are supported by complementary experimental results. They were rationalized on the basis of electronegativity, potential involvement in the bonding of valence d-orbitals and atom size. TD-DFT calculations showed that the effect of doping on optical properties is sizable and this should stimulate research on the modulation of luminescence properties in the dithiolato and diseleno families of complexes.

Metalcyclopentadienyl complexes (MCp) + (M = Fe, Ru, Os) bound to the large polyaromatic hydrogenated hydrocarbon (PAH) C 96 H 24 used as a model for pristine graphene have been studied using a density functional theory (DFT) generalized gradient approximation (PBE functional) to reveal their structural features and dynamic behavior. The inter-ring haptotropic rearrangements (IRHRs) for these complexes were shown to occur via two transition states and one intermediate. The energy barriers of the η 6 ⇌ η 6 IRHRs of the (MCp) + unit were found to be 30, 27, and 29 kcal/mol for M = Fe, Ru, and Os, respectively. These values are significantly lower than the values found previously for smaller PAHs. Both polar and nonpolar solvents were found not to affect significantly the energy barrier heights. Investigated transition metal complexes could be used in general as catalysts in the design of novel derivatives or materials with promising properties. Metalcyclopentadienyl complexes (MCp) + of PAHs show catalytic properties mainly due to their structural details as well as their important characteristic of inter-ring haptotropic rearrangement. IRHRs take place usually by intramolecular mechanisms. During IRHRs, the ML n organometallic groups (OMGs) undergo shifting along the PAH plane and could coordinate additional reagents, which is important for catalysis. Large PAHs such as graphene, fullerenes, and nanotubes possess intrinsic anticancer activity, and numerous arene complexes of Ru and Os have been proven to have anticancer properties as well. We suppose that coordinating Ru or Os to very large PAHs could synergistically increase the anticancer activity of resulting complexes.

Coinage-metal atomically precise nanoclusters are made of a well-defined metallic core embedded in a ligand-protecting outer shell. Whereas gold derivatives are particularly well documented, examples of silver nanoclusters are somewhat limited and copper species remain particularly scare. Our DFT relativistic calculations on superatomic metallic cores indicate that copper species are almost as stable as gold clusters and more stable than their silver counterparts. Thus, for silver superatomic cores, the role of the stabilizing ligands is more crucial in the stabilization of the overall structure, in comparison to copper and gold. Hence, the chemistry of the earlier counterparts of gold, especially copper, should grow quickly with at least characterizations of species related to that found in the heavier elements in the triad, which requires tackling synthetic challenges. Time-dependent (TD)-DFT calculations show that with an increase of the cluster core nuclearity, the absorption bands are redshifted, allowing us to differentiate between the clusters types. Moreover, the optical properties of the silver cores are fairly different from that of their Cu and Au relatives., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)