This thesis is an investigation into the hydrogenous behavior of Zintl phases. Zintl phases are comprised of an active metal (i.e alkali, alkaline earth, and rare earth) and a p-block element. The discussion gives an overview of the influence hydrogen affects the electronic and geometric structure of Zintl phases and subsequent properties. Incorporation of hydrogen into a Zintl phase is categorized as either polyanionic or interstitial Zintl phase hydrides. In the former the hydrogen covalently bonds to the polyanion and in the latter the hydrogen behaves hydridic, coordinates exclusively with the active metal, leading to an oxidation of the polyanion. Synthesis of hydrogenous Zintl phases may be through either a direct hydrogenation of a Zintl phase precursor or by combining active metal hydrides and p-block elements. The latter strategy typically leads to thermodynamically stable hydrides, whereas the former supports the formation of kinetically controlled products. 

Polyanionic hydrides are exemplified by SrAlGeH and BaAlGeH. The underlying Zintl phases SrAlGe and BaAlGe have a structure that relates to the AlB₂ structure type. These Zintl phases possess 9 valence electrons for bonding and, thus, are charge imbalanced species. Connected to the charge imbalance are superconductive properties (the T_c of SrAlGe and BaAlGe is 6.7 and 6.3 °C, respectively). In the polyanionic hydrides the hydrogen is covalently bonded as a terminating ligand to the Al atoms. The Al and Ge atoms in the anionic substructure [AlGeH]^2- form corrugated hexagon layers. Thus, with respect to the underlying Zintl phases there is only a minimal change to the arrangement of metal atoms. However, the electronic properties are drastically changed since the Zintl phase hydrides are semiconductors. 

Interstitial hydrides are exemplified by Ba₃Si₄H_x (1 < x < 2) which was obtained from the hydrogenation of the Zintl phase Ba₃Si₄. Ba₃Si₄ contains a Si₄^6- “butterfly” polyanion. Hydrogenation resulted in a disordered hydride in which blocks of two competing tetragonal structures are intergrown. In the first structure the hydrogen is located inside Ba₆ octahedra (I-Ba₃Si₄H), and in the second structure the hydrogen is located inside Ba₅ square pyramids (P-Ba₃Si₄H₂). In both scenarios the “butterfly anions appear oxidized and form Si₄^4- tetrahedra.

Hydrogenation may also be used as a synthesis technique to produce p-block element rich Zintl phases, such as silicide clathrates. During hydrogenation active metal is removed from the Zintl phase precursor as metal hydride. This process, called oxidative decomposition, was demonstrated with RbSi, KSi and NaSi. Hydrogenation yielded clathrate I at 300 °C and 500 °C for RbSi and KSi, respectively. Whereas a mixture of both clathrate I and II resulted at 500 °C for NaSi. 

Low temperature hydrogenations of KSi and RbSi resulted in the formation of the silanides KSiH₃ and RbSiH₃. These silanides do not represent Zintl phase hydrides but are complex hydrides with discrete SiH₃^- complex species. KSiH₃ and RbSiH₃ occur dimorphic, with a disordered α-phase (room temperature; SG Fm-3m) and an ordered β-phase (below -70 °C; SG = Pnma (KSiH₃); SG = P2₁/m ( RbSiH₃)). During this thesis the vibrational properties of the silyl anion was characterized. The Si–H stretching force constants for the disordered α-phases are around 2.035 Ncm^-1 whereas in the ordered b-forms this value is reduced to ~1.956 Ncm^-1. The fact that SiH₃^- possesses stronger Si-H bonds in the α-phases was attributed to dynamic disorder where SiH₃^- moieties quasi freely rotate in a very weakly coordinating alkali metal ion environment.