Bonding interactions of metal clusters [Mn (M= Cu, Ag, Au; n=1-4)] with ammonia. Are the metal clusters adequate as a model of surfaces?

Abstract

Cálculos de densidade funcional (B3LYP/LANL2DZ) para clusters metálicos de amônia foram efetuados para obter comprimentos de ligação, modos de estiramento vibracional M-N, energias de ligação, cargas atômicas de Mulliken e potenciais adiabáticos de ionização. Os resultados indicam que átomos de cobre formam ligações mais intensas com amônia do que com prata ou ouro. A interação da ligação Ag n com amônia é a mais fraca de todos os sistemas. A ligação das moléculas de amônia à clusters metálicos é comparável à de sistemas piridina-M n. Ambas moléculas apresentam uma interação dativa do par de elétrons isolado no átomo de nitrogênio. Cargas atômicas de Mulliken mostram uma pequena transferência de carga da molécula NH 3 para o átomo metálico ou cluster, sugerindo a formação da ligação dativa. Depois da transferência de carga da molécula de amônia, os clusters metálicos sofrem uma redistribuição das cargas e isto pode ser importante na estabilização do sistema. Na superfície, a redistribuição de carga deve ser menos significativa. Nesse sentido, o uso de clusters metálicos como modelo de superfície pode ser um modelo inadequado.Density Functional (B3LYP/LANL2DZ) calculations for ammonia metal clusters were done in order to obtain bond lengths, M-N stretching vibrational modes, binding energies, Mulliken atomic charges and adiabatic ionization potentials. The results indicate that copper atom forms stronger bonds with ammonia than silver or gold. The bond interaction between Ag n and ammonia is the weakest of all the systems. The bond of the ammonia molecule to the metal clusters can be compared with the pyridine-M n systems. Both molecules present a donation interaction from the lone-pair of electrons on the nitrogen atom. Mulliken atomic charges show a small charge transfer from the NH 3 molecule to the metal atom or cluster, suggestive of a dative bond formation. After the charge transfer from the ammonia molecule, the metal clusters undergo a redistribution of the charge and this could be important for the stabilization of the system. In a surface, the redistribution of the charge should be less significant. In this sense, the use of metal clusters as a model of the surface may be an inadequate model. Keywords: metal clusters, bond lengths, M-N stretching vibrational modes, binding energies, Mulliken atomic charges and adiabatic ionization potentials IntroductionComplexes of bare metal clusters with simple molecules are important model systems for fundamental studies of metal-ligand bonding in cluster and surface chemistry. 1-17Of particular interest is the relationship between cluster and bulk surface chemistry. In this area, Mitchell et al. 15 studied the reactions of copper and silver dimers with ammonia in the gas phase, while Chan and Fournier 17 reported a theoretical study of the binding of ammonia to small copper and silver clusters. A simple picture of the bonding mechanism was reported, and comparisons were made between ammonia adsorbed on the metal atoms and on bulk surfaces.The theoretical study...

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“…Several early investigations have demonstrated the reactivity of metal clusters with ammonia, − an example of which is shown in Figure , where the interesting clusters Al 11 NH 3 – and Al 12 NH 3 – dominated the products. Theoretical calculations revealed that the presence of ammonia leads to geometric distortion of Al 12 – together with dissociation of the NH 3 molecule, the N and H atoms of which transfer onto the Al cluster, resulting in a reorganized minimum-energy structure.…”

Mechanistic Insights about Electrochemical Proton-Coupled Electron Transfer Derived from a Vibrational Probe

“…This distance is consistent with previously calculated bond lengths of amines on Ag surfaces. 59,60 The presence of a covalent Ag−N bond in this configuration is further supported by the charge transfer between Ag(100) and the amine, as indicated by the charge density difference relative to the potential of zero free charge (PZFC) (Figure 5a). A covalent bond is also supported by the observed population of Ag−N bonding orbitals below the Fermi level, as determined from crystal orbital Hamilton population analysis (SI, Figure S5).…”

A hybrid organic–inorganic three-dimensional cathode interfacial material for organic solar cells

“…29 These are likely to originate from chelation of the metal surface by the lone electron pair on the nitrogen and the accompanying interfacial polarization effects. [44][45][46] Indeed, SKPM measurements on freshly evaporated gold coated by our interlayers presented dipole shis of À0.6 up to À0.7 eV, regardless of the chemical and physical (linear or three dimensional) structures of the interlayers. Similar to the gold interface, comparable interfacial dipoles are expected for the interfaces between the interlayer materials and the evaporated aluminium electrode.…”