Impurity Electron Localization in Early-Transition-Metal-Doped Gold Clusters

Abstract

We have performed x-ray absorption spectroscopy of size selected, free, cationic, transition-metal-doped (Sc, Ti, V, Cr) gold clusters in a size range n = 1 − 9. The electronic configuration of the impurity atom was determined by modeling the x-ray absorption spectrum in a charge-transfer-multiplet framework which makes it possible to quantify the amount of localization of the impurity 3d states. Depending on the dopant element and the host cluster size we find a wide variety in the behavior of local electronic structures. ScAu + n clusters show strong hybridization of the scandium 3dstates with the host electronic states except for ScAu + 1 where we find a completely localized 3d electron. In TiAu + n clusters a pronounced odd-even alternation is present in the local electronic structure of the impurity atom. The 3d occupation number of the titanium dopant is approximately 2 and 1.6 electrons in odd and even numbered clusters, respectively. In CrAu + n clusters the electronic structure of the dopant is governed by shell closure of the gold host which leads to almost unperturbed 3d states in CrAu + n , n = 2, 6, 8 and hybridization of the 3d-states in CrAu + n , n = 1, 5, 7. Contrary to the other systems investigated the 3d occupation of 3.3 electrons in VAu + n clusters is independent of the cluster size. Only in special cases we find an integer number of localized 3d impurity electrons. Furthermore, in all cases the local electronic structure of the dopant does not strongly depend on the exact coordination of the dopant atom.This finding allows for a better understanding of the bonding beyond a simple shell model approach with its ad hoc assumption of integer numbers of delocalized impurity electrons.

Electronic and Geometric Effects on Chemical Reactivity of 3d-Transition-Metal-Doped Silver Cluster Cations toward Oxygen Molecules

“…This study pointed out that the clusters tend to encourage delocalization of 3d electrons when a closed electronic shell is formed. More recently, the problems of s–d electron interaction in size-selected clusters have been studied by X-ray spectroscopy on transition-metal-doped gold cluster ions to probe a local magnetic moment and electronic configuration of the dopant atom. , A computational study has been reported on Ag N V + clusters to show size-dependent evolution in the geometric and electronic structures . Corresponding anionic clusters have been studied as well by photoelectron spectroscopy. − …”

Relativistic Effects Stabilize the Planar Wheel-like Structure of Actinide-Doped Gold Clusters: An@Au7 (An = Th to Cm)

“…The closest competitor, ISO2, is 17.7 kcal/mol more unstable than the lowest one, confirming the high stability of the planar wheel-like structure of UAu 7 . In contrast to the UAu 7 , the global minimum of WAu 7 is found to be a planar structure with C 2 v symmetry, displaying a different geometrical structure in comparison to early-transition-metal-doped Au 7 compounds, such as three-dimensional structures of CrAu 7 + or TiAu 7 + . Importantly, the D 7 h planar structure for WAu 7 at 17.7 kcal/mol is found not to be a stationary structure with six negative vibrational frequencies, which spontaneously optimizes to the minima with C 2 v symmetry and 4 B 2 spin state.…”

“…For decades, plenty of investigations on searching gold-containing new materials due to their fascinating structural variety and roles in catalysis, and its capability of accommodating dopant elements to form metallic alloys or semi-conducts, which is ascribed to that gold enables to form the strong covalent bonds most elements in the periodic table, , which has expanded from transition metals − to alkali metals to p-block elements, , even to rare-earth elements. ,, Due to the aromaticity-induced stability, the open-shell Au 7 , featuring a coplanar structure with a C 2 v symmetry could perform as a ligand in the design of novel materials . Such investigations on MAu 6 (M = Ti; V; Cr) by computational chemistry and spectroscopic chemistry have revealed that these species have planar structures with the open-shell transition-metal atom located in the planar center .…”