Synthesis and crystal structure of a salt containing _∞¹{Zn[trans-μ₂(η³: η³-Ge₉)]}^2- anions: A polymer with Ge ₉ zintl clusters bridged by Zn atoms

The reaction of an ethylenediamine (en) solution of K₄Ge ₉ with Zn₂(Mesnacnac)₂ {Mesnacnac = [(2,4,6-Me₃C₆H₂)NC(Me)]₂CH} in the presence of 18-crown-6 (18-crown-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane) leads to the formation of the new compound [K(18-crown-6)]₂{Zn[trans- μ₂(η³:η³-Ge₉)]}(en). A crystallographic structure determination revealed that the salt contains _∞¹[Zn(Ge₉)]^2- polyanions in which each Zn atom bridges two Ge₉ clusters by coordinating to opposite triangular faces of the Ge₉ deltahedra. The polymeric chain can be formally described as consisting of a trans Zn^II complex with two [η³:η³-Ge₉]^4- ligands. ¹H NMR spectroscopic investigations indicated that the protonation of the Mesnacnac^- ligand by the solvent ethylenediamine plays a crucial role in the disproportionation of the Zn^I starting material and thus in the formation of the polymeric Zn^II complex. In contrast, the reaction of ZnPh₂ instead of Zn₂(Mesnacnac)₂ under the same conditions leads to the known complex [PhZn(η⁴- Ge₉)]^3-. Crystals of the compound [K(18-crown-6)] ₂{Zn[trans-μ₂(η³:η³- Ge₉)]}(en), containing strands of _∞ ¹{Zn[trans-μ₂(η³:η³- Ge₉)]}^2- units in which Zn atoms connect Ge₉ clusters in an η³-fashion, were obtained by the reaction of the binary Zintl phase K₄Ge₉ with Zn₂(Mesnacnac) ₂ (Mesnacnac = [(2,4,6-Me₃C₆H ₂)NC(Me)]₂CH) in ethylenediamine (en).