Surface modifications of eight-electron palladium silver superatomic alloys.

Atomically precise thiolate-protected coinage metal nanoclusters and their alloys are far more numerous than their selenium congeners, the synthesis of which remains extremely challenging. Herein, we report the synthesis of a series of atomically defined dithiophosph(in)ate protected eight-electron superatomic palladium silver nanoalloys [PdAg20{S2PR2}12], 2a-c (where R = OiPr, a; OiBu, b; Ph, c) via ligand exchange and/or co-reduction methods. The ligand exchange reaction on [PdAg20{S2P(OnPr)2}12], 1, with [NH4{Se2PR2}12] (where R = OiPr, or OnPr) leads to the formation of [PdAg20{Se2P(OiPr)2}12] (3) and [PdAg20{Se2P(OnPr)2}12] (4), respectively. Solid state structures of 2a, 2b, 3 and 4 unravel different PdAg20 metal frameworks from their parent cluster, originating from the different distributions of the eight-capping silver(I) atoms around a Pd@Ag12 centered icosahedron with C2, D3, Th and Th symmetries, respectively. Surprisingly ambient temperature crystallization of the reaction product 3 obtained by the ligand exchange reaction on 1 has resulted in the co-crystallization of two isomers in the unit cell with overall T (3a) and C3 (3b) symmetries, respectively. To our knowledge, this is the first ever characterized isomeric pair among the selenolate-protected NCs. Density functional theory (DFT) studies further rationalize the preferred geometrical isomerism of the PdAg20 core.

Alloying dichalcogenolate-protected Ag21 eight-electron nanoclusters: a DFT investigation.

The isoelectronic doping of dichalcogenolato nanoclusters of the type [Ag21{E2P(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@M12-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.

All-selenolate-protected eight-electron platinum/silver nanoclusters.

The first atomically and structurally precise platinum/silver superatoms protected by Se-donor ligands were synthesized in high yield by adopting ligand replacements on [PtAg20{S2P(OnPr)2}12] (3) with 12 equiv. of di-alkyl diselenophosph(in)ates. Structures of [PtAg20{Se2P(OR)2}12] (R = nPr (1a), iPr (1b)) and [PtAg20{Se2P(CH2CH2Ph)2}12] (2) were accurately determined by single-crystal X-ray diffraction to reveal an eight-electron [Pt@Ag12]4+ icosahedral core embedded within a cube of eight silver(i) atoms and wrapped into a shell of 12 diselenophosph(in)ates. While the lowest energy absorption band of the Se derivatives is red-shifted to longer wavelengths in comparison with the S analogue, it is blue-shifted in the emission spectra. Density functional theory (DFT) and TD-DFT calculations rationalize the electronic structures as those of eight-electron superatoms, with their HOMO and LUMO being the 1P and 1D levels, respectively. The two UV-visible lowest bands are associated with 1P → 1D metal to metal charge transfer (MMCT) transitions. The blue shift observed for the S analogue results from a larger HOMO-LUMO gap in the case of dithiolate ligands.

Homoleptic Platinum/Silver Superatoms Protected by Dithiolates: Linear Assemblies of Two and Three Centered Icosahedra Isolobal to Ne2 and I3.

Three bimetallic platinum/silver nanoclusters, PtAg20(dtp)12 (1), Pt2Ag33(dtp)17 (2), and Pt3Ag44(dtp)22 (3) (dtp: dipropyl dithiophosphate), with cluster electron counts of 8, 16, and 22, respectively, were produced via a one-phase coreduction method. Single-crystal X-ray structures reveal that their inner cores can be visualized as consisting of one, two, and three centered icosahedral Pt@Ag12 units, respectively. In 2 and 3, these units are vertex-sharing and are assembled linearly. Intriguingly, the 22-electron alloy (3) is isolobal to the linear triiodide anion, I3-, and represents the first example of a cluster made of three superatoms whose bonding characteristics are similar to those of a triatomic molecular species.

Mono- and hexa-palladium doped silver nanoclusters stabilized by dithiolates.

The synthesis, via a co-reduction method, of the first Pd-containing silver-rich 21-metal-atom nanocluster passivated by dithiolates, [PdAg20{S2P(OnPr)2}12] (1), is reported. 1 is an 8 electron superatom isoelectronic to [Ag21{S2P(OiPr)2}12]+. The doping of Pd in 1 leads to its high stability against degradation in solution and shows red emission in MeTHF at 77 K. In addition, we report the X-ray crystal structure of a multi-palladium doped silver nanocluster, [Pd6Ag14(S){S2P(OnPr)2}12] (2), for the first time. Its X-ray structure exhibits a sulfide-centered Pd6Ag2 rhombohedron surrounded by twelve additional silver atoms with S6 symmetry. The XPS study and DFT calculations indicate that 2 contains Pd(0) and Ag(i) metals. A significant decrease in the electrochemical gap was observed in the SWVs of 2.