Pnictogen-based Zintl phases

The quite large but still emerging family of polar intermetallic compounds inspired our research towards a more complete understanding of these phases that often reward us by being structurally, geometrically or electronically beyond the expectations of even the most imaginative mind. We started by studying the binary systems A − Pn (A = alkali metal; Pn = As, Sb, Bi). Surprisingly, even in such systems, thought to be known, new compounds with unexpected features could be found, as shown in the first part of the dissertation with the compounds A₃Bi₂ and A₅Pn₄, two rare “metallic salts” made of dimers [Bi₂]2− and flat tetramers [Pn₄]4−, respectively, both containing an extra delocalized electron. In a second part, we complemented the list of already known indium-arsenides: Cs₅In₃As₄ with a remarkable structure made of two coexisting polymorphic forms of different dimensionality, containing layers and chains of [In₃As₄] 5− and KBa₂InAs₃ where isolated [In ₂As₇]13− and the 1D-polymer [In ₂As₅]7− are found.; In the last part of this thesis, and what constitutes the major accomplishment of this work, is presented the first results obtained in an extremely promising family of niobium-arsenides. Our systematic studies led to the discovery of many compounds with diverse characteristics but all based on the stability of the tetrahedral unit NbAs₄. Examples are: (a) K₃₈ Nb₇As₂₄, Cs₉Nb₂As₆ and K₉Nb₂As₆, the first mixed-valence transition-metal Zintl phases with dimers of [NbVNb IVAs₆]9−; (b) K₆NbAs ₅, K₆NbTlAs₄ and K₈NbPbAs₅ where one of the edges of the NbAs₄ unit is bridge by additional arsenic, thallium and lead, respectively; (c) Cs₇NbIn ₃As₅, exhibiting a cubane-like anion of [NbIn₃As ₄] with a handle of arsenic; (d) Cs₂₄Nb₂In ₁₂As₁₈ in which two cubane-like anions are connected to each other.; Our studies have been fruitful but however encompass only a small area of the large family of transition metals Zintl phases. These examples illustrate well the richness of this particular system. Without a doubt, if investigations are extended to other transition metals and more complex systems of mixed alkali and alkaline earth metals, numerous new phases could be unveiled.