A new type of Zintl phase is presented that contains endohedrally filled clusters and that allows for the formation of intermetalloid clusters in solution by a one-step synthesis. The intermetallic compound K(5-x)Co(1-x)Sn(9) was obtained by the reaction of a preformed Co-Sn alloy with potassium and tin at high temperatures. The diamagnetic saltlike ternary phase contains discrete [Co@Sn(9)](5-) clusters that are separated by K(+) ions. The intermetallic compound K(5-x)Co(1-x)Sn(9) readily and incongruently dissolves in ethylenediamine and in the presence of 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (2.2.2-crypt), thereby leading to the formation of crystalline [K([2.2.2]crypt)](5)[Co(2)Sn(17)]. The novel polyanion [Co(2)Sn(17)](5-) contains two Co-filled Sn(9) clusters that share one vertex. Both compounds were characterized by single-crystal X-ray structure analysis. The diamagnetism of K(5-x)Co(1-x)Sn(9) and the paramagnetism of [K([2.2.2]crypt)](5)[Co(2)Sn(17)] have been confirmed by superconducting quantum interference device (SQUID) and EPR measurements, respectively. Quantum chemical calculations reveal an endohedral Co(1-) atom in an [Sn(9)](4-) nido cluster for [Co@Sn(9)](5-) and confirm the stability of the paramagnetic [Co(2)Sn(17)](5-) unit.

The accessibility of triads with deltahedral Zintl clusters in analogy to fullerene-linker-fullerene triads is another example for the close relationship between fullerenes and Zintl clusters. The compound {[K(2.2.2-crypt)]4[RGe9-CH=CH-CH=CH-Ge9R]}(toluene)2 (R=(2Z,4E)-7-amino-5-aza-hepta-2,4-dien-2-yl), containing two deltahedral [Ge9] clusters linked by a conjugated (1Z,3Z)-buta-1,3-dien-1,4-diyl bridge, was synthesized through the reaction of 1,4-bis(trimethylsilyl)butadiyne with K4Ge9 in ethylenediamine and crystallized after the addition of 2.2.2-cryptand and toluene. The compound was characterized by single-crystal structure analysis as well asNMR and IR spectroscopy.

Silicon is the most important material for solar cells. However, its low conversion rate/quantum efficiency requires a rather high material consumption. Thus, researchers undertake enormous experimental and theoretical efforts to find alternative Si allotropes with a better efficiency and in the ideal case a direct electronic band gap. In recent years and months many new allotropic Si structures have been reported; however, they are often described incoherently and without context to existing structures. Our approach allows a classification of many of these allotropes and a relation of their structures to substructures of, for example, known Zintl phases. For this so-called "chemi-inspired" search for promising Si structures we present a "construction kit" as a guide to introducing a large number of tetrahedral Si allotropes, all derived by a modification of the pristine cubic diamond structure. In addition, this approach allows us to realize structural (topological) relationships between experimentally accessible Zintl phases of different composition, such as open tetrahedral frameworks, to a yet unknown extent, including even known phase transitions of specific Zintl phases. In topological, structural, and computational analyses (on a DFT-PBE0/SVP level of theory) we show the close relationship of ten low-energy Si structures derived from the cubic diamond modification; five of them are new, and some show quasi-direct band gaps. A simple deviation of this approach enables the construction of many more tetrahedral structures.

The number of Zintl phases containing polyhedral clusters of tetrel elements that are accessible for chemical reactions of the main-group element clusters is rather limited. The synthesis and structural characterization of two novel ternary intermetallic phases A(14)ZnGe(16) (A = K, Rb) are presented, and their chemical reactivity is investigated. The compounds can be rationalized as Zintl phases with 14 alkali metal cations A(+) (A = K, Rb), two tetrahedral [Ge(4)](4-) Zintl anions, and one anionic heterometallic [(Ge(4))Zn(Ge(4))](6-) cluster per formula unit. The Zn-Ge cluster comprises two (Ge(4)) tetrahedra which are linked by a Zn atom, with one (Ge(4)) tetrahedron coordinating with a triangular face (η(3)) and the other one with an edge (η(2)). [(η(3)-Ge(4))Zn(η(2)-Ge(4))](6-) is a new isomer of the [(Ge(4))Zn(Ge(4))](6-) anion in Cs(6)ZnGe(8). The phases dissolve in liquid ammonia and thus represent rare examples of soluble Zintl compounds with deltahedral units of group 14 element atoms. Compounds with tetrahedral [E(4)](4-) species have previously been isolated from solution for E = Si, Sn, and Pb, and the current investigation provides the "missing link" for E = Ge. Reaction of an ammonia solution of K(14)ZnGe(16) with MesCu (Mes = 2,4,6-(CH(3))(3)C(6)H(2)) in the presence of [18]-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) yielded crystals of the salt [K([18]-crown-6)](2)K(2)[(MesCu)(2)Ge(4)](NH(3))(7.5) with the polyanion [(MesCu)(2)Ge(4)](4-). This MesCu-stabilized tetrahedral [Ge(4)](4-) cluster also completes the series of [(MesCu)(2)Si(4-x)Ge(x)](4-) clusters, which have previously been isolated from solution for x = 0 and 0.7, as the end member with x = 4. The electronic structures of [(Ge(4))Zn(Ge(4))](6-) and [(MesCu)(2)Ge(4)](4-) were investigated in terms of a molecular orbital description and analyses of the electron localization functions. The results are compared with band structure calculations for the A(14)ZnGe(16) phases (A = K, Rb).

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