Synthesis and structure of [K+-(2,2)diaza-[18]-crown-6][K3Ge9]•2ethylenediamine:: Stabilization of the two-dimensional layer 2∞[K3Ge91-]

Large bright-red, transparent crystalline plates of [K-(2,2)diaza-[18]-crown-6]K3Ge9. 2en are obtained, in high-yield, from a reaction of (2,2)diaza-[18]-crown-6 in toluene with a solution of K4Ge9/potassium metal (K) in ethylenediamine (en). The compound crystallizes in the monoclinic space group P2(1)/m (a = 10.740(1) Angstrom, b = 15.812(1) Angstrom, c = 12.326(1) Angstrom, beta = 114.74 degrees; Z = 2). The crystal structure of [K-(2,2)diaza-[18]-crown-6]K3Ge9. 2en features two-dimensional [K3Ge9] layers formed by uncomplexed K+ cations and Ge-9(4-) anions. The "not-so-bare" cluster compound features a unique Ge-9(4-) cluster that exhibits a slightly distorted C-2v geometry that is closer to D-3h than the expected C-4v. Use of noncryptand sequestering agents in the isolation of Ge cluster anions from en solutions opens new avenues in understanding important cation-anion interactions in the stability and reactivity of Zintl ions, as well as a viable route to isolating Zintl anions with higher charges per atom.