Synthesis and Characterization of the New Lead Strontium Germanate PbSrGeO₄

Abstract

The new lead strontium germanate PbSrGeO4 was synthesized by a high-temperature solid-state reaction of lead(II) oxide, strontium carbonate, and germanium(IV) oxide at a temperature of 900 °C in a platinum crucible. The compound crystallizes in the orthorhombic space group P212121 (no. 19) being isotypic to the structure of BaNdGaO4 [1]. The primitive cell contains four formula units with lattice parameters of a = 995:40(2), b = 732:44(2), c = 599:42(2) pm, V = 437:02(2)Å3, and residuals of R1 = 0:0385 and wR2 = 0:0997 for all data. The main structural element of PbSrGeO4 is an isolated [GeO4]4- tetrahedron. A circular arrangement of six of these [GeO4]4- tetrahedra leads to the formation of large channels along b in which the strontium cations are eightfold coordinated by oxygen atoms. The lead cations are coordinated by three oxygen atoms, and with a lone pair of electrons they show a pseudo-tetrahedral coordination. Next to the structural investigations, PbSrGeO4 was characterized by Raman-spectroscopic investigations and DFT calculations.

Synthesis and characterization of PbBaGeO4

“…The germanium-oxygen bond lengths inside the tetrahedra vary from 173.6(11) to 177.2(10) pm with a mean value of 176.1 pm, and the O-Ge-O bond angles range from 106.2(5) to 116.2(7)° (average value: 109.5°). Bond lengths and angles are comparable with other compounds containing GeO 4 tetrahedra[3,16,17].…”

“…1 was thoroughly hand milled using an agate mortar, and placed in a FKS 95/5 crucible (Feinkornstabilisiert, 95 % Pt, 5 % Au, Ögussa, Wien, Austria) for the heating procedure. 3 2…”

“…The interatomic lead-oxygen distances in the coordination sphere range from 224.5(9) to 234.7(11) pm (mean value: 231.2 pm) whereby the Pb 2+ cation is shifted out of the central position in the opposite direction of the lone-pair. The behavior of the lead cation in the presence of a stereochemically active electron lone-pair is well known from PbSrGeO 4 [3] where even the electron localization function (ELF) was calculated. The interatomic barium-oxygen distances are between 261.6(11) and 293.7 (11) …”

“…According to the systematic extinctions, the orthorhombic space group P2 1 2 1 2 1 was derived. Due to the fact that PbBaGeO 4 is isotypic to PbSrGeO 4 [3], the structural refinement was performed by taking the positional parameters of PbSrGeO 4 as starting values (Shelxl-13 [9,10]). All atoms were refined with anisotropic displacement parameters, and the final difference Fourier synthesis did not reveal any significant residual peaks.…”

“…Taking a common flux consisting of lead(II) and lead(IV) oxide, as already used in the high-pressure synthesis of the rareearth borogermanate Ce 6 (BO 4 ) 2 Ge 9 O 22 [1], we obtained a biphasic product. The probe consisted of the well-known lead germanate Pb 5 Ge 3 O 11 [2] and the lead strontium germanate PbSrGeO 4 [3]. Obviously, the flux material also acted as a reaction partner.…”