The primary goal of this research project is to develop methodologies for further functionalization of Zintl clusters in order to attach more than two substituents. Progress was made in a step by step manner as follows: (a) develop methodology for the synthesis of Zintl clusters functionalized with more than two substituents, (b) carry out subsequent studies for the properties of the functionalized clusters and their reactivity, and (c) introduce more organic functionalities to the cluster core. Each of these segments is discussed in detail in this dissertation.After introducing the background of Zintl ions and the recent developments on the study of nine–atom germanium clusters (Chapter 1), the rational synthesis of tri–silylated Ge9 clusters is discussed (Chapter 2). This approach allows for Ge9 clusters with more than two substituents to be synthesized by reacting "hypersilyl" chloride (Me3Si)3SiCl with acetonitrile suspension of the intermetallic precursor K4Ge9 to form [Ge9(Si(SiMe3)3)3]–. Our investigations show this route to be general and applicable to a variety of R3SiCl, with R = Et, iPr, nBu and Ph, etc. Following the rational synthesis of [Ge9(Si(SiMe3)3)3]–, the preparation of tetra–substituted Ge9 clusters was studied next, and this is discussed in detail in Chapter 3. Reactions between K[Ge9(Si(SiMe3)3)3] and R3SnCl (R = Me, nBu and Ph) result in the addition of the –SnR3 fragment to the tri–silylated Ge9 clusters and the formation of neutral tetra–substituted species [Ge9(Si(SiMe3)3)3(SnR3)]0. Dynamic behavior of the fourth substituent was observed in solution, and this is interpreted as the –SnR3 fragment migrating along the three germanium atoms within the triangular base.Studying the similarity in the reactivity of functionalized Ge9 clusters and the naked parent Ge94– anions has both experimental and theoretical implications. The results presented in Chapter 4 demonstrate that like the naked cluster Ge94–, Tl atom could be added to one of the square faces of [Ge9(Si(SiMe3)3)3]– to form a tri–substituted ten–atom closo–cluster [Ge9Tl(Si(SiMe3)3)3]0. Intermolecular dynamic behavior was observed and was studied by NMR investigations. It can be rationalized by a "Tl+ dissociation–association" mechanism.Chapter 5 describes the addition of a variety of alkyl groups to the already tri–functionalized species by the reactions between [Ge9(Si(SiMe3)3)3]– and R–X undergoing SN2 mechanism. [Ge9(Si(SiMe3)3)3Et]0 was crystallized and structurally characterized. An intramolecular dynamic behavior was observed in solution and theoretical study was carried out for clarifying its pathway.Chapter 6 investigates the reactivity of [Ge9(Si(SiMe3)3)3]– towards transition metal complexes. It turns out that naked transition metal atoms tend to interact with the triangular prismatic bases of the tri–silylated monoanion. [(Ge9R3)CuI(Ge9R3)(CuIPPh3)]0 and [(Ge9R3)Pd0(Ge9R3)]2– (R = –Si(SiMe3)3) were synthesized and structurally characterized through such investigations.Chapter 7 presents further studies of the nucleophilic reactivity of organo–Zintl clusters. A variety of main group and alkyl halides are shown to react with organo–Zintl clusters such as [Ge9(CH=CH–Ph)2]2–, [Ge9(Adm)2]2–, [Ge9(tBu)]3–, etc. We believe this can be developed into a general tool for synthesizing fully organically functionalized Zintl clusters. The dissertation ends with a summary and a discussion of future prospects, primarily focused on the fields of embedding clusters with useful functionalities and expanding the synthetic methodology into other intermetallic systems.