Hyper trumps super: A central atom, typically a metal, surrounded by halogen or oxygen atoms is called a superhalogen. Theoretical calculations and experiments reveal that a new class of highly electronegative species can be created when the central metal atom is surrounded by superhalogen moieties. These hyperhalogens can have electron affinities even larger than those of their superhalogen building blocks.

We report the discovery of a new class of clusters consisting of Au(n)(BO(2)) that forms during the oxygenation of gold clusters when boron nitride is used as insulation in a pulsed-arc cluster ion source (PACIS). Photoelectron and mass spectroscopy of these clusters further revealed some remarkable properties: instead of the expected Au(n)O(m) peaks, the mass spectra contain intense peaks corresponding to Au(n)(BO(2)) composition. Some of the most predominant features of the electronic structure of the bare Au clusters, namely even-odd alternation in the electron affinity, are preserved in the Au(n)(BO(2)) species. Most importantly, Au(n)(BO(2)) [odd n] clusters possess unusually large electron affinity values for a closed-shell cluster, ranging from 2.8-3.5 eV. The open-shell Au(n)(BO(2)) [even n] clusters on the other hand, possess electron affinities exceeding that of F, the most electronegative element in the periodic table. Using calculations based on density functional theory, we trace the origin of these species to the unusual stability and high electron affinity of the BO(2) moiety. The resulting bond formed between BO(2) and Au(n) clusters preserves the geometric and electronic structure of the bare Au(n) clusters. The large electron affinity of these clusters is due to the delocalization of the extra electron over the Au(n) cluster.

The equilibrium structure, stability, and electronic properties of the Al(13)X (X=H,Au,Li,Na,K,Rb,Cs) clusters have been studied using a combination of photoelectron spectroscopy experiment and density functional theory. All these clusters constitute 40 electron systems with 39 electrons contributed by the 13 Al atoms and 1 electron contributed by each of the X (X=H,Au,Li,Na,K,Rb,Cs) atom. A systematic study allows us to investigate whether all electrons contributed by the X atoms are alike and whether the structure, stability, and properties of all the magic clusters are similar. Furthermore, quantitative agreement between the calculated and the measured electron affinities and vertical detachment energies enable us to identify the ground state geometries of these clusters both in neutral and anionic configurations.

The geometric and electronic structures of gas phase (M03S3)nS2 and (M0 3 S 3)1I_1(MoS4h clusters with n = 2, 3, 4, ... are studied experimentally using mass and photoelectron spectroscopy. The M0 3 S 3 units form one-dimensional chains with length 'n'. There are two possible types of terminations at the ends: a single S atom or a MoS 4 cluster. The experimental results are compared to calculations based on density-functional theory. Although clusters of this type have been known for decades as constituents of Chevrel phases, we here report their first gas phase synthesis for sizes up to n = 17. With increasing n, the gap vanishes extending such clusters to a conducting wire.

The structural and electronic properties of neutral and anionic molybdenum sulfide clusters with the composition Mo 3 S n (n ¼ 0-12) were studied by density-functional calculations. The theoretical results are confirmed by a comparison with photoelectron spectra of the corresponding W 3 S n À anions providing experimental values for the vertical detachment energies (VDEs) and the highest occupied (HOMO) and lowest unoccupied (LUMO) gaps. For sulfur contents up to n ¼ 9 the clusters are composed of a central Mo 3 unit, which is decorated by bridging, terminal, and three-fold coordinated S atoms. For n > 9, a cleavage of the Mo 3 center is observed. The formation of disulfide like ions is found for Mo 3 S 9 and larger species. In accordance with investigations of MoS n , Mo 2 S n , and Mo 4 S n clusters, the heat of formation and the VDE reaches a maximum in the sulfur-rich region beyond the composition Mo:S ¼ 1:2. [8]. Both free and adsorbed small Mo m S n clusters exhibit either a three-dimensional structure based on a Mo m framework or a platelet-shaped geometry derived from the layered MoS 2 bulk structure [9,10]. With the help of density-functional calculations on Mo m S n (m ¼ 1, 2, and 4) clusters, the cluster-platelet transition could be related to a sulfur excess of the system of at least one additional S atom per MoS 2 formula unit, i.e., to MoS 3 [9,11,12]. Among the small, Mo-rich Mo m S n clusters, Mo 4 S 6 , a Mo 4 tetrahedron bridged by six S atoms along the edges, was found to be the most exceptionally stable compound both by theory and experiment [9][10][11][12][13]. The large calculated energy gap of 3 eV between the highest occupied (HOMO) and the lowest unoccupied (LUMO) cluster state