On the Mechanism of Connecting Deltahedral Zintl Clusters via Conjugated Buta-1,3-dien-1,4-diyl Functionalities: Synthesis and Structure of [Ge₉−CH=CH−CH=CH−Ge₉]⁶⁻

We report on the synthesis and structure, as well as on the mechanism of formation of the [Ge₉−CH=CH−CH=CH−Ge₉]⁶⁻ unit. As shown by in situ NMR spectroscopy (¹H, COSY, HSQC, HMBC), both (1Z,3Z)- and (1E,3Z)-[Ge₉−CH=CH−CH=CH−Ge₉]⁶⁻ are formed during the reaction of a mixture of 1,4-bis(trimethylsilyl)butadiyne and A₄Ge₉ (A=K, Rb) with ethylenediamine. However, upon layering of the obtained solution with 222-crypt/toluene (222-crypt=4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo-[8.8.8]hexacosan) only the (1Z,3Z)-isomer crystallizes as {[A(222-crypt)]₆[(1Z,3Z)-(Ge₉−CH=CH−CH=CH−Ge₉)]}(tol)₂(en)₂ (A=K, Rb) salts. Single crystals of these salts were characterized by X-ray structure analysis and Raman spectroscopy, indicating the presence of three superimposed conformers of (1Z,3Z)-[Ge₉−CH=CH−CH=CH−Ge₉]⁶⁻, which show different orientations of the cluster units with respect to the planar (1Z,3Z)-buta-1,3-dien-1,4-diyl linker unit.