Exploring the low-lying structures of Aun(CO)+ (n = 1–10): adsorption and stretching frequencies of CO on various coordination sites

Adsorption of CO on cationic gold clusters is insensitive to the structural details of the adsorption site.

Pd(n)Ag(4-n) and Pd(n)Pt(4-n) clusters on MgO (100): a density functional surface genetic algorithm investigation

The novel surface mode of the Birmingham Cluster Genetic Algorithm (S-BCGA) is employed for the global optimisation of noble metal tetramers upon an MgO (100) substrate at the GGA-DFT level of theory. The effect of element identity and alloying in surface-bound neutral subnanometre clusters is determined by energetic comparison between all compositions of PdnAg(4-n) and PdnPt(4-n). While the binding strengths to the surface increase in the order Pt > Pd > Ag, the excess energy profiles suggest a preference for mixed clusters for both cases. The binding of CO is also modelled, showing that the adsorption site can be predicted solely by electrophilicity. Comparison to CO binding on a single metal atom shows a reversal of the 5σ-d activation process for clusters, weakening the cluster-surface interaction on CO adsorption. Charge localisation determines homotop, CO binding and surface site preferences. The electronic behaviour, which is intermediate between molecular and metallic particles allows for tunable features in the subnanometre size range.

Gas-phase synthesis and structure of Wade-type ruthenium carbonyl and hydrido carbonyl clusters

The gas-phase reaction of size-selected Ru(n)(+) (n = 4-6) clusters with CO in an ion trap yields only one specific ruthenium carbonyl complex for each cluster size, Ru4(CO)14(+), Ru5(CO)16(+), and Ru6(CO)18(+). First-principles density functional theory calculations reveal structures for these hitherto unknown carbonyl compounds that are in perfect agreement with the geometries predicted by Wade's electron counting rules. Furthermore, reactions with D2 show that for Ru4(+) and Ru6(+), CO molecules can be partially replaced by D2 to form hydrido carbonyl complexes while preserving the total ligand count corresponding to the Wade cluster sizes.

Rapid hydrogenation: perfect quasi architecture (Ag@SiO2NPs) as a substrate for nitrophenol reduction

Spherical nanoparticles with core-frame architecture are a viable route to combine multiple functionalities on a nanoscopic scale.

Noble metal alloy clusters in the gas phase derived from protein templates: unusual recognition of palladium by gold

Matrix assisted laser desorption ionization of a mixture of gold and palladium adducts of the protein lysozyme (Lyz) produces naked alloy clusters of the type Au24Pd(+) in the gas phase. While a lysozyme-Au adduct forms Au18(+), Au25(+), Au38(+) and Au102(+) ions in the gas phase, lysozyme-Pd alone does not form any analogous cluster. Addition of various transition metal ions (Ag(+), Pt(2+), Pd(2+), Cu(2+), Fe(2+), Ni(2+) and Cr(3+)) in the adducts contributes to drastic changes in the mass spectrum, but only palladium forms alloys in the gas phase. Besides alloy formation, palladium enhances the formation of specific single component clusters such as Au38(+). While other metal ions like Cu(2+) help forming Au25(+) selectively, Fe(2+) catalyzes the formation of Au25(+) over all other clusters. Gas phase cluster formation occurs from protein adducts where Au is in the 1+ state while Pd is in the 2+ state. The creation of alloys in the gas phase is not affected whether a physical mixture of Au and Pd adducts or a Au and Pd co-adduct is used as the precursor. The formation of Au cores and AuPd alloy cores of the kind comparable to monolayer protected clusters implies that naked clusters themselves may be nucleated in solution.

Copper doping of small gold cluster cations: influence on geometric and electronic structure

The effect of Cu doping on the properties of small gold cluster cations is investigated in a joint experimental and theoretical study. Temperature-dependent Ar tagging of the clusters serves as a structural probe and indicates no significant alteration of the geometry of Au(n) (+) (n = 1-16) upon Cu doping. Experimental cluster-argon bond dissociation energies are derived as a function of cluster size from equilibrium mass spectra and are in the 0.10-0.25 eV range. Near-UV and visible light photodissociation spectroscopy is employed in conjunction with time-dependent density functional theory calculations to study the electronic absorption spectra of Au(4-m)Cu(m) (+) (m = 0, 1, 2) and their Ar complexes in the 2.00-3.30 eV range and to assign their fragmentation pathways. The tetramers Au(4) (+), Au(4) (+)[middle dot]Ar, Au(3)Cu(+), and Au(3)Cu(+)[middle dot]Ar exhibit distinct optical absorption features revealing a pronounced shift of electronic excitations to larger photon energies upon substitution of Au by Cu atoms. The calculated electronic excitation spectra and an analysis of the character of the optical transitions provide detailed insight into the composition-dependent evolution of the electronic structure of the clusters.

Dopant-induced 2D-3D transition in small Au-containing clusters: DFT-global optimisation of 8-atom Au-Ag nanoalloys

A genetic algorithm (GA) coupled with density functional theory (DFT) calculations is used to perform global optimisations for all compositions of 8-atom Au-Ag bimetallic clusters. The performance of this novel GA-DFT approach for bimetallic nanoparticles is tested for structures reported in the literature. New global minimum structures for various compositions are predicted and the 2D-3D transition is located. Results are explained with the aid of an analysis of the electronic density of states. The chemical ordering of the predicted lowest energy isomers are explained via a detailed analysis of the charge separation and mixing energies of the bimetallic clusters. Finally, dielectric properties are computed and the composition and dimensionality dependence of the electronic polarizability and dipole moment is discussed, enabling predictions to be made for future electric beam deflection experiments.

Interaction of carbon monoxide with small metal clusters: a DFT, electrochemical, and FTIR study

The adsorption of CO molecules onto small metal clusters was studied using density functional theory (DFT) calculations, and experimental electrochemical and attenuated total reflection-Fourier transform infrared spectroscopic (ATR-FTIR) techniques were used to examine CO adsorbed onto nanostructures of similar composition. The adsorption strengths and CO vibrational stretching frequencies were calculated and analyzed for clusters of the form M–CO for all of the period 4, 5, and 6 d-block transition metals. A direct link between the νCO and the population of d orbitals of the metal was observed. All possible binding sites for CO on clusters of the form Pd4–CO, Pd2Pt2–CO, and Pd2Au2–CO were determined and the corresponding adsorption energies and CO stretching frequencies were examined. Pure Pd and bimetallic PdPt and PdAu nanostructures were fabricated and used as catalysts for the adsorption and electrochemical oxidation of CO. The relative quantities of CO molecules adsorbed to surface of the catalysts decrease in the order of PdPt > Pd > PdAu, consistent with our DFT results. The location of νCO bands of CO adsorbed onto the nanostructured catalysts were determined by means of ATR-FTIR spectroscopy and were found to have values close to that predicted by DFT. This paper shows that DFT calculations on very small metal clusters Mn–CO (n ≤ 4) can be a simple but effective way of screening catalysts for their adsorbing properties.