Clusters constitute an intermediate state of matter between molecules and solids whose properties are size dependent and can be tailored. In recent years, cluster science has become one of the most exciting areas of research since their study can not only bridge our understanding between atoms and their bulk but also between various disciplines. In addition, clusters can serve as a source of new materials with uncommon properties. This dissertation deals with an in-depth study of clusters as a bridge across physics, chemistry, and materials science and provides a fundamental understanding of the structure-property relationships by focusing on three different topics. The first topic deals with superatoms which are clusters that mimic the chemistry of atoms. I show that superhalogens and superalkalis can be designed to mimic the chemistry of halogen and alkali atoms, respectively. An entirely new class of salts can then be synthesized by using these superatoms as the building blocks. I have also explored the possibility of designing highly electronegative species called hyperhalogens by using superhalogens as ligands or superalkalis as core and a combination of both. Another aspect of my work on superatom is to examine if traditional catalysts (namely Pd) can be replaced by clusters composed of earthabundant elements (namely Zr and O). This is accomplished by comparing the electronic structure and reactivity of Pd clusters with isoelectronic ZrO clusters. The second topic deals with a study of the electronic structure of coinage metal (Cu and Ag) clusters and see if they remain unchanged when a metal atom is replaced by an isoelectronic hydrogen atom as is the case with Au-H clusters. The third topic deals with clusters as model of polymeric materials to understand their gas storage and sequestration properties. This is accomplished by studying the trapping of H2, CO2, CH4 and SO2 molecules in borazine-linked polymers (BLPs) and benzimidazole-linked polymers (BILPs). The first two topics provide a bridge between physics and chemistry, while the third topic provides a bridge to materials science.

Electron affinity is one of the most important parameters that guide chemical reactivity. Halogens have the highest electron affinities among all elements. A class of molecules called superhalogens has electron affinities even greater than that of Cl, the element with the largest electron affinity (3.62 eV). Traditionally, these are metal-halogen complexes which need one electron to close their electronic shell. Superhalogens have been known to chemistry for the past 30 years and all superhalogens investigated in this period are either based on the 8-electron rule or the 18-electron rule. In this work, we have studied two classes of unconventional superhalogens: borane-based superhalogens designed using the Wade-Mingo’s rule that describes the stability of closo-boranes, and pseudohalogen based superhalogens. In addition, we have shown that superhalogens can be utilized to build hyperhalogens, which have electron affinities exceeding that of the constituent superhalogens, and also to stabilize unusually high oxidation states of metals.

Organic molecules are known for their stability due to aromaticity. Superhalogens, on the other hand, are highly reactive anions, whose electron affinity is larger than that of chlorine. This thesis, using first principles calculations, explores possible methods for creation of superhalogen aromatic molecules while attempting to also develop a fundamental understanding of the physical properties behind their creation. The first method studied uses anionic cyclopentadienyl and enhances its electron affinity through ligand substitution or ring annulation in combination with core substitutions. The second method studies the possibilities of using benzene, which has a negative electron affinity (EA), as a core to attain similar results. These cases resulted in EAs of 5.59 eV and 5.87 eV respectively, showing that aromaticity rule can be used to create strong anionic organic molecules. These studies will hopefully lead to new advances in the development of organic based technology.