Tetrarubidium nonagermanide(4-) ethylenediamine, Rb4[Ge9][en]

Abstract

Orange crystals of Rb4[Ge9][en] are obtained after the exchange reaction of a solution of ‘NaGe2.25' (precursor) in ethylenediamine (en) with solid RbI at 363 K, followed by slow cooling. The compound is very sensitive to oxidation and hydrolysis. The thermal decomposition in dynamic vacuum starts at 350 K with the complete loss of en followed by the sublimation of Rb in four steps (Rb8Ge25, Rb8Ge44, RbxGe136 with x ≤ 16, Ge). The Raman spectrum shows the characteristic bands of the [Ge9]4– anion (151, 163, 185 and 222 cm–1). Rb4[Ge9][en] crystallizes in a new structure type (space group P21/m; a = 15.353 Å, b = 16.434 Å, c = 15.539 Å, β = 113.75°; Z = 6; Pearson code mP198-40), which can be described as a hierarchical derivative of the structures of Al4YbMo2 and CrB4 (initiators) formed by partial atom-to-aggregate replacement: B4[□][Cr] ≙ Al4[Yb][Mo]2 ≙ Rb4[Ge9][en]1–2. Three crystallographic independent [Ge9]4– clusters with different orientations are embedded in a 4-connected 465 net formed by the Rb atoms, a network of condensed tetraasteranes. The clusters are distorted monocapped tetragonal antiprisms with D1(Ge–Ge) = 2.57 Å (16 Ç ) and D2(Ge–Ge) = 2.84 Å (4 Ç ). The atoms of clusters with D1 and D2 lie at the surface of a rotational ellipsoid (a = b = 2.136 Å, c = 2.431 Å). The en molecules are located in open channels along [1¯ 0 1]. The coordinations [Ge9] Rb12/4 and Rb [Ge9]4/12 en2/8 show that the first step of solvation do not separate the cations from the cluster anions.