The closo-Ge5 2- Anion: Synthesis, Crystal Structure, and Raman Spectrum of (2,2,2-crypt-K+)2Ge5 2-·THF

The isolation and structural characterization of the closo-Ge5 2- cluster anion by X-ray crystallography and Raman spectroscopy is reported, completing the series of five-atom homopolyatomic anions of the group 14 elements, M5 2- (M = Ge, Sn, Pb). The closo-Ge5 2- anion was obtained as the (2,2,2-crypt-K+)2Ge5 2-·THF salt which crystallizes in the triclinic system, space group P1, in a unit cell of dimensions a = 10.9657(4) Å, b = 12.1750(5) Å, c = 12.9142(5) Å, α = 62.163(1)°, β = 67.776(1)°, and γ = 84.187(1)°. The trigonal bipyramidal geometry observed for the Ge5 2- anion (∼D 3 h point symmetry) is in accord with that predicted by Wade's rules for a 2n + 2 skeletal electron system and has been observed for the Sn5 2- and Pb5 2- homologues and for the isovalent Tl5 7- and Bi5 3+ ions. The Raman spectrum of the Ge5 2- anion is compared and assigned by analogy with that of the Bi5 3+ cation.