Two-dimensional magic numbers in mass abundances of photofragmented bimetallic clusters

Abstract

The stability of cationic gold clusters doped with one transition metal atom was investigated by a mass spectrometric analysis of fragments resulting from high fluence irradiation of a cluster beam. Strongly enhanced abundances are found for Au5X+, X = V, Mn, Cr, Fe, Co, Zn, which implies that these species are far more stable towards fragmentation than their neighbouring cluster sizes. Here we interpret the enhanced stability of these clusters within a shell model approach for two-dimensional (2D) systems: the number of delocalized electrons in Au5X+ is six, which is a magic number for 2D systems. Quantum chemical calculations for Au N Zn+ (N = 2-6) predict planar structures that are stabilized by the influence of the dopant atom. Also, the main features of the calculated molecular orbitals are well reproduced by a simple electron-in-a-box model. The present report constitutes the first observation of 2D magic numbers in size dependent properties of metal clusters.

The Cu7Sc Cluster is a Stable σ‐Aromatic Seven‐Membered Ring

“…[19] Recently, this model has also been extended to planar metal clusters. [20] In this case, the number of electrons which yields a closed electronic shell depends on the shape of the cluster. In the case of triangular or rectangular clusters, enhanced stabilities are expected for structures having 2, 6, 8, 12, 16 or 20 delocalized valence s-electrons, whereas the number of these electrons is 2, 6, 10, 12, 16 or 20 for circular clusters.…”

Size‐Dependent Structural Evolution and Chemical Reactivity of Gold Clusters

“…On the other hand, the size range of our jellium picture can be easily extended for other regularly shaped clusters; for example, the planarity in the size range n = 4-13 atoms is related to magic numbers of 2, 6, and 12 electrons (see, for instance, refs. [36,37]). For these clusters, the triangular Au 6 À , with its seven delocalized electrons, has a very low vDE [27] (characteristic for a cluster just past a shell closing, similar to the behavior of Au 20 À discussed above) and the triangular Au 10 À , with 11 delocalized electrons, has an anomalously high vDE [27] (characteristic for a cluster approaching shell closure, that is, 12 e À in 2D, in analogy with the behavior of the 3D cluster Au 16 À ).…”

Far‐Infrared Spectra of Yttrium‐Doped Gold Clusters AunY (n=1–9)

“…[27,48] The enhanced abundance for Au 5 X + , where X = V, Cr, Mn, Fe, Co, and Zn, was rationalized in terms of their planarity in combination with the six delocalized electrons being a magic number for 2D systems. [49,50] In this series of photofragmentation mass spectrometry experiments strong abundance enhancements also were observed for 16-atom gold-cluster cations doped with a trivalent metal (Sc, Y, Nb). [48,51,52] The enhanced stability corresponds to an 18-electron shell closure which is strengthened by a winebottle-type mean-field potential resulting from the endohedral position of the dopant atom in the gold.…”