This award in the Inorganic, Bioinorganic and Organometallic Chemistry program supports research by Professor Slavi Sevov at Notre Dame University on the reactivity of main-group deltahedral clusters (Zintl ions), both homo- and hetero-atomic (including a number of recently discovered bismuth/transition metal species). Using a variety of organic halides and alkynes, a variety of organic groups will be added to nine-atom germanium clusters [Ge9]n- (n = 4, 3, 2). The products of these reactions are mono- and di-substituted clusters [R-Ge9]3- and [R-Ge9-R]2-, respectively, where the R groups can be simple alkyl groups or can have double bonds, phenyl or pyridine rings, and other functionalities. These studies will be extended into the other elements of this group, which form the same nine-atom clusters, i.e. [Si9]n-, [Sn9]n-, and [Pb9]n-, as well as into heteroatomic clusters such as ([Ge9]-x[Snx])n-, (In4Bi5)3-, and (Tl4Bi5)3-. The proposed reactions focus on the organic substituents and take advantage of well-studied reactions in other areas of chemistry such as organic and organometallic chemistry by applying the accumulated knowledge to the new substrates. For example, the double bonds in alkenyl-Zintl ions such as [CH2=CH-Ge9-CH=CH2]2- may be susceptible to hydroboration and/or polymerization. Pyridine-substituted Zintl ions may be able to coordinate to transition metals via the pyridine nitrogen and to form molecular or extended structures. The relation between the geometry and bonding of small molecular clusters, and their properties and reactivity will be investigated.
The proposed clusters are of interest as potential precursors to new classical materials (intermetallics, extended structures) as well as nano materials (nanorods, thin films, surface grafting) with novel electronic and magnetic properties. The project will be used as a tool to attract both students and postdoctoral fellows from underrepresented groups through a relationship with the Graduate Education for Minorities organization. Relationships are also being developed with the predominantly minority Clark University (Atlanta), Xavier (New Orleans), and St. Mary and St. Edward colleges (San Antonio) in order to bring summer undergraduate students and to recruit graduate students from these universities.
The general theme of the research of this project is about the chemistry, i.e. behavior, of a class of elements when they are forced to carry unusual for them charges. The elements are the main-group metals and semimetals that come after the transition elements in the Periodic Table, and we have studied their chemistry when the carry the unusual for them negative charges. Thus, we have found that Si, Ge, Sn, and Pb cluster together to form nine-atom spherical species with 4- charge, e.g. Ge94-. We have extensively studied how these latter species react with other agents. We have found out that they can: (a) attach up to three groups on the outside (Figure 1), (b) exchange up to two atoms for atoms from the next group to the right (Figure 2), (c) add a tenth vertex (Figure 3), and (d) form heteroatomic clusters mixing with other elements of the same group (Figure 4). Previously we have also shown that transition-metal atoms can be inserted inside the clusters, transition-metal organometallic fragments can be added to the clusters, and that two or more clusters can be linked to form longer formations. All these results show that such negatively-charged species of metals and semimetals have very rich, unexpected, and exciting chemistry. They also indicate a very fertile area for further exploration.
