Published: August 09, 2011 r2011 American Chemical Society 10276 dx.doi.org/10.1021/jp207474h | J. Phys. Chem. A 2011, 115, 10276–10280 ARTICLE pubs.acs.org/JPCA Electronic Structure Similarities in Pb x Sb y À and Sn x Bi y À Clusters Joshua J. Melko, † Ute Werner, ‡ Roland Mitri  c, § Vlasta Bona  ci  c-Kouteck y,* ,‡,|| and A. W. Castleman, Jr.* ,†,^ † Departments of Chemistry, and ^ Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, United States ‡ Institut f€ ur Chemie, Humboldt-Universit € at zu Berlin, Brook-Taylor-Strasse 2, 12489 Berlin, Germany § Fachbereich Physik, Freie Universit € at Berlin, Arnimallee 14, 14195 Berlin, Germany ) Interdisciplinary Center for Science and Technology, University of Split, Mestrovicevo Setaliste bb, 21000 Split, Croatia b S Supporting Information 1. INTRODUCTION While nanoscale clusters have served as valuable models for investigating various fundamental molecular interactions, 1 with the growth of nanoscience they are gaining increased interest as systems with practical applications. 2 This is particularly evident in clusters of the p-block elements, where the discovery of C 60 has led to a new field of materials in fullerenes and carbon nanotubes, while IIIÀV semiconductor materials have led to numerous modern electronics. Recently, we have started to explore the new area of cluster assembled materials, which allows the fine-tuning of material properties based on the characteristics of the constituent cluster building blocks. 3 In this realm, het- eroatomic p-block clusters have proven to be especially interest- ing, as their heteroatomic nature provides a facile route to manipulating the charge state and size of the cluster building blocks, while changing the electronic structure in a predictable way. 4 This has led to many new clusters being identified as suitable candidates for assembly into nanomaterials. 5 One intri- guing class of clusters, termed “superatoms”, has been shown to mimic the properties of elements. 6 These superatoms offer many possibilities in designing new materials based on traditional rules of chemistry. Recently, in some systems it has been found that the electronic structure between atoms and isoelectronic molecular counterparts 7 may be comparable, providing new superatoms on the basis of parallel electronic structures. Sepa- rately, similarities in isoelectronic clusters have been observed in reactivity studies, where neutral systems are shown to possess the same structural features and radical oxygen centers as their charged counterparts. 8 These findings have spurred our interest in investigating the electronic structures of other isoelectronic species. The p-block clusters provide a good opportunity to explore this phenomenon because of their facile synthesis in experiment 4,5 and their promise for success in the realm of cluster assembled materials. 3 Additionally, the current applications of materials built from p-block elements already carry importance and span a broad range of disciplines. 9 In the present study, we employ photoelectron spectroscopy experiments and theoretical calculations to explore electronic structure similarities between Pb x Sb y À and Sn x Bi y À clusters. These IVÀV elements are next to each other on the periodic table, so equivalent stoichiometries lead to equivalent valence electron counts. However, our results indicate that some of these clusters also have similar electronic structures and analogous ground-state geometries. An additional focus of the present work is to determine what factors govern when similarities persist and when they break down. Our experimental and theoretical results indicate that the electronic structure is quite sensitive to changing the total number of valence electrons. Further, theore- tical calculations depict how changing the ground-state geometry can affect the electronic structures. Although these findings may be expected, we have also found that the electronic structures of unrelated clusters can be similar, provided the valence electron count and geometric structures are analogous. In fact, there is a substantial body of work in the literature involving photoioniza- tion or electron-induced dissociation experiments on isovalent heteroatomic clusters, 10,11 where comparable mass spectra dis- tributions point to similar geometric structures and growth patterns (even for Pb x Sb y and Sn x Bi y clusters). 12 Perhaps the best example is the work by Recknagel et al., 11 which concludes Received: August 4, 2011 ABSTRACT: The geometric and electronic structure of Pb x Sb y À and Sn x Bi y À clusters are investigated by photoelectron spectroscopy and theoretical methods. It is found that PbSb 2 À and SnBi 2 À have similar spectroscopic patterns, reflecting correlations in electronic nature that are a result of their isoelectronic character and common geometries. Analogous findings are presented for Pb 2 Sb 2 À and Sn 2 Bi 2 À . Further, we investigate the effect of altering the total valence count, and separately the geometry, on spectroscopic patterns. We conclude that these heavy p-block elements are interchangeable and that the electronic structure correspondence can be preserved regardless of elemental composition. This represents an extension of the traditional concepts of periodicity, where elements of similar valence configuration are grouped into columns. Instead, elements from different columns may be combined to yield similarities in chemistry, given the overall valence count is preserved.