The closo-Ge-5(2-) anion: Synthesis, crystal structure, and Raman spectrum of (2,2,2-crypt-K+)(2)Ge-5(2-)center dot THF

The isolation and structural characterization of the closo-Ge-5(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, M-5(2-)(M = Ge, Sn, Pb). The closo-Ge-5(2-) anion was obtained as the (2,2,2-crypt-K+)(2)Ge-5(2-). THF salt which crystallizes in the triclinic system, space group P1, in a unit cell of dimensions a = 10.9657(4) Angstrom, b = 12.1750(5) Angstrom, c = 12.9142(5) Angstrom, alpha = 62.163(1)degrees, beta = 67.776(1)degrees, and gamma = 84.187(1)degrees. The trigonal bipyramidal geometry observed for the Ge-5(2-) anion (similar to D-3h 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 Sn-5(2-) and Pb-5(2-) homologues and for the isovalent Tl-5(7-) and Bi-5(3+) ions. The Raman spectrum of the Ge-5(2-) anion is compared and assigned by analogy with that of the Bi-5(3+) cation.