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 180cm-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 P3̄cl (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.