Hydride-Containing Pt-doped Cu-rich Nanoclusters: Synthesis, Structure, and Electrocatalytic Hydrogen Evolution.

A structurally precise hydride-containing Pt-doped Cu-rich nanocluster [PtH2 Cu14 {S2 P(Oi Pr)2 }6 (CCPh)6 ] (1) has been synthesized. It consists of a bicapped icosahedral Cu14 cage that encapsulates a linear PtH2 unit. Upon the addition of two equivalents of CF3 COOH to 1, two hydrido clusters are isolated. These clusters are [PtHCu11 {S2 P(Oi Pr)2 }6 (CCPh)4 ] (2), which is a vertex-missing Cu11 cuboctahedron encaging a PtH moiety, and [PtH2 Cu11 {S2 P(Oi Pr)2 }6 (CCPh)3 ] (3), a distorted 3,3,4,4,4-pentacapped trigonal prismatic Cu11 cage enclosing a PtH2 unit. The electronic structure of 2, analyzed by Density Functional Theory, is a 2e superatom. The electrocatalytic activities of 1-3 for hydrogen evolution reaction (HER) were compared. Notably, Cluster 2 exhibited an exceptionally excellent HER activity within metal nanoclusters, with an onset potential of -0.03 V (at 10 mA cm-2 ), a Tafel slope of 39 mV dec-1 , and consistent HER activity throughout 3000 cycles in 0.5 M H2 SO4 . Our study suggests that the accessible central Pt site plays a crucial role in the remarkable HER activity and may provide valuable insights for establishing correlations between catalyst structure and HER activity.

Hydride-containing 2-Electron Pd/Cu Superatoms as Catalysts for Efficient Electrochemical Hydrogen Evolution.

The first hydride-containing 2-electron palladium/copper alloys, [PdHCu11 {S2 P(Oi Pr)2 }6 (C≡CPh)4 ] (PdHCu11 ) and [PdHCu12 {S2 P(Oi Pr)2 }5 {S2 PO(Oi Pr)} (C≡CPh)4 ] (PdHCu12 ), are synthesized from the reaction of [PdH2 Cu14 {S2 P(Oi Pr)2 }6 (C≡CPh)6 ] (PdH2 Cu14 ) with trifluoroacetic acid (TFA). X-ray diffraction reveals that the PdHCu11 and PdHCu12 kernels consist of a central PdH unit encapsulated within a vertex-missing Cu11 cuboctahedron and complete Cu12 cuboctahedron, respectively. DFT calculations indicate that both PdHCu11 and PdHCu12 can be considered as axially-distorted 2-electron superatoms. PdHCu11 shows excellent HER activity, unprecedented within metal nanoclusters, with an onset potential of -0.05 V (at 10 mA cm-2 ), a Tafel slope of 40 mV dec-1 , and consistent HER activity during 1000 cycles in 0.5 M H2 SO4 . Our study suggests that the accessible central Pd site is the key to HER activity and may provide guidelines for correlating catalyst structures and HER activity.

Synthesis and Luminescence Properties of Two-Electron Bimetallic Cu-Ag and Cu-Au Nanoclusters via Copper Hydride Precursors.

The synthesis, structural characteristics, and photophysical properties of luminescent Cu-rich bimetallic superatomic clusters [Au@Cu12(S2CNnPr2)6(C≡CPh)4]+ (1a+), [Au@Cu12{S2P(OR)2}6(C≡CPh)4]+ (2+), (2a+ = iPr; 2b+ = nPr), [Au@Cu12{S2P(C2H4Ph)2}6(C≡CPh)4]+ (2c+), and [Ag@Cu12{S2P(OnPr)2}6(C≡CPh)4]+ (3+) were studied. Compositionally uniform clusters 1+-3+ were isolated from the reaction of dithiolato-stabilized, polyhydrido copper clusters with phenylacetylene in the presence of heterometal salts. By using X-ray diffraction, the structures of 1a+, 2a+, 2b+, and 3+ were able to be determined. ESI-mass spectrometry and elemental analysis confirmed their compositions and purity. The structural characteristics of these clusters are similar with respect to displaying gold (or silver)-centered Cu12 cuboctahedra surrounded by six dithiocarbamate/dithiophosph(in)ate and four alkynyl ligands. The doping of Au and Ag atoms into the polyhydrido copper nanoclusters significantly enhances their PL quantum yields from Ag@Cu12 (0.58%) to Au@Cu12 (55%) at ambient temperature in solution. In addition, the electrochemical properties of the new alloys were investigated by cyclic voltammetry.

Copper Clusters Containing Hydrides in Trigonal Pyramidal Geometry.

Structurally precise copper hydrides [Cu11H2{S2P(OiPr)2}6(C≡CR)3], R = Ph (1), C6H4F (2), and C6H4OMe (3), were first synthesized from the polyhydrido copper cluster [Cu20H11{S2P(OiPr)2}9] with nine equivalents of terminal alkynes. Later, their isolated yields were significantly improved by direct synthesis from [Cu(CH3CN)4](PF6), [NH4][S2P(OiPr)2], NaBH4, and alkynes along with NEt3 in THF. 1, 2, and 3 were fully characterized by single-crystal X-ray diffraction, ESI-MS, and multinuclear NMR spectroscopy. All three clustershave 11 copper atoms, adopting 3,3,4,4,4-pentacapped trigonal prismatic geometry, with two hydrides inside the Cu11 cage, the position of which was ascertained by a single-crystal neutron diffraction structure of cluster 1 co-crystallized with a [Cu7(H){S2P(OiPr)2}6] (4) cluster. Six dithiophosphate and three alkynyl ligands stabilize the Cu11H2 core in which the two hydrides adopt a trigonal pyramidal coordination mode. This coordination mode is so far unprecedented for hydride. The 1H NMR resonance frequency of the two hydrides appears at 4.8 ppm, a value further confirmed by 2H NMR spectroscopy for their deuteride derivatives [Cu11(D)2{S2P(OiPr)2}6(C≡CR)3]. A DFT investigation allows understanding the bonding within this new type of copper(I) hydrides.

Locating Interstitial Hydrides in MH2@Cu14 (M = Cu, Ag) Clusters by Single-Crystal X-ray Diffraction.

Two structures, [Cu15H2(S2CNnBu2)6(C≡CPh)6][CuCl2] (1) and [AgH2Cu14{S2P(OiPr)2}6(C≡CPh)6][PF6] (2), are characterized by X-ray crystallography with high-quality single crystals. The position of interstitial hydrides can be accurately located. In addition, the refinement of the hydrides with anisotropic displacement parameters (ADPs) was successful. The distances between the central atom and copper atoms, as well as the distances within the metal cages surrounding the hydrides, are analyzed and compared with similar MH2@Cu14 (M = Cu, Ag, Pd) compounds. This work provides a thoughtful and accurate assessment of the considerations and challenges associated with anisotropic refinement for H atoms, particularly in X-ray data collection.