The [Sn5]2- cluster compound [K-(2,2,2-crypt)]2Sn5 - synthesis, crystal structure, Raman spectrum, and hierarchical relationship to CaIn2

Abstract

Dark red crystals of [K-(2,2,2)-crypt)]2Sn5 precipitate after the reaction of (2,2,2)-crypt with a solution of K1.33Sn in liquid ammonia at room temperature. The compound is sensitive to oxidation and hydrolysis. The sequence of Raman bands (104, 120, 133 and 180 cm–1) is characteristic for the trigonal bipyramidal closo-[Sn5]2– cluster anion. The wave numbers correspond with the data from Hartree-Fock calculations (114, 128, 142 and 187 cm–1). The compound crystallizes trigonally (a = 11.736 Å, c = 22.117 Å, Z = 2, space group P3c1 (No. 165); Pearson code hP262), isotypic with [Na-(2,2,2)-crypt)]2Pb5. The atoms of the cluster show strange anisotropic displacements, which are perfectly reducible to a helical rigid-body motion around and along [001] (libration: ± 9.5°; translation ± 0.29 Å). The structure can be described as a hierarchical derivative of the initiator CaIn2 (P63/mmc, hP6), generated by an atom-to-aggregate replacement: [Ca][In]2 = [Sn5][K @ C36H72N4O12]2. Thus, the distribution of the [Sn5]2– Zintl anions is hexagonal primitive, and the cation complexes are located close to the centers of trigonal superprisms formed by Sn5 clusters.