Synthesis of Zintl Triads Comprising Extended Conjugated π‑Electronic Systems: [RGe₉–CHCH–CHCH–Ge₉R]^4– (R = −CHCH₂, −C(CH₃)CH–CHN(CH₂)₂NH₂)

Triads with extended conjugated π-electronic systems between polyhedral cage molecules possess promising electronic properties. In contrast to the known fullerene–bridge–fullerene triads, fewer synthetic procedures are known for the related homoatomic deltahedral cage molecules of the heavier homologues of carbon. The synthesis of the organo-Zintl triads [RGe₉–CHCH–CHCH–Ge₉R]^4– with R = −CHCH₂ (R₁), −C­(CH₃)CH–CHN­(CH₂)₂NH₂ ((2<i>Z</i>,4<i>E</i>)-7-amino-5-azahepta-2,4-dien-2-yl) (R₂) is reported, in which the deltahedral Ge₉ cages carry an additional functional group, allowing for further connections. Both anionic cage entities bear a butadiene-1,4-diyl bridge which is formed by reacting the Zintl ion [Ge₉]^4– with 1,4-bis­(trimethylsilyl)­butadiyne in ethylenediamine. The organic tethers can be attached by nucleophilic attack of the Ge₉ clusters at the bis­(trimethylsilyl)­acetylene and (3<i>Z</i>/3<i>E</i>)-7-amino-1-(trimethylsilyl)-5-azahepta-3-en-1-yne, respectively, in ethylenediamine, and the products <i>cis</i>/<i>trans</i>-[R₁Ge₉–CHCH–CHCH–Ge₉R₁]^4– and <i>cis</i>/<i>cis</i>-[R₂Ge₉–CHCH–CHCH–Ge₉R₂]^4– have been isolated as [<i>A</i>(2,2,2-crypt)]⁺ salts with <i>A</i> = K, Rb, respectively. Crystals containing the novel anions [RGe₉–CHCH–CHCH–Ge₉R]^4– have been structurally characterized by X-ray diffraction methods, and the compounds have been investigated by ¹H and ¹³C NMR as well as by Raman spectroscopy. The <i>cis</i>/<i>cis</i> configurational isomer of [R₁Ge₉–CHCH–CHCH–Ge₉R₁]^4– was characterized by means of NMR spectroscopy. Via in situ NMR measurements, we shed some light on the formation of the Zintl triads [RGe₉–CHCH–CHCH–Ge₉R]^4– bearing supplemental organic tethers