Mixed Valence and Unusual Germanium Coordination in SrGe₈As₁₀, BaGe₈As₁₀, and BaGe₇P₁₂

Abstract

The new Zintl-compounds AEGe 8 As 10 (AE = Sr, Ba) and BaGe 7 P 12 were synthesized via solid-state reactions, and their structures were determined by single crystal and powder X-ray diffraction. SrGe 8 As 10 and BaGe 8 As 10 crystallize in the space group Cmce and show complex 3D networks composed of three different Ge−As motifs and As−As bonds with mixed valence of germanium in the oxidation states +2, + 3, and +4. Mixed valences of germanium +3 and +4 occur in BaGe 7 P 12 , which crystallizes in the space group R3̅ with a 3D network built up of Ge 2 P 6 dumbbells and P−P bonds. An exceptional 6-fold coordinated germanium resides in the center of a GeP 6 trigonal antiprism. High temperature X-ray diffraction shows thermal stabilities up to 923−953 K. UV−Vis and resistivity measurements reveal a semiconducting nature with small indirect band gaps between 0.02 and 1.6 eV. Electronic band structure calculations confirm the semiconducting state and indicate covalent bonds within the Ge-Pn polyanions.

Two-Dimensional and Three-Dimensional Tetrel-Arsenide Frameworks Templated by Li and Cs Cations

“…Of the five Ge sites, four are tetrahedrally coordinated, while the fifth is tri-coordinated. The formation of a tri-coordinated germanium allows for the anionic layers to accommodate extra electrons donated from the cation and is commonly observed in ternary germanium pnictide phases. ,,,,, …”

New Noncentrosymmetric Tetrel Pnictides Composed of Square‐Planar Gold(I) with Peculiar Bonding

“…This solution showed a fully occupied Au site and a mixed occupancy of the 8 f Ge/As site, with site occupancy factors of 0.6(1)/0.4, respectively. Despite the mixed occupancy of Ge and As being reported, [19] in most cases, Ge and As prefer to occupy separate atomic sites [20–25] . In the NCS space group Cc (no.…”

“…Despite the mixed occupancy of Ge and As being reported, [19] in mostc ases, Ge and As prefer to occupy separate atomic sites. [20][21][22][23][24][25] In the NCS space group Cc (no. 9), there are three fully occupied 4a sites (1 Au, 1G e, 1A s).…”

High Thermoelectric Properties in the Sodalite Compounds BaGe8As14 and AGe7As15 (A = Rb, Cs)

“…The electronic band gaps extracted from Arrhenius plots give very small activation energies of 0.008 and 0.002 eV for RbGe 7 As 15 and CsGe 7 As 15 , respectively (Figure b). This indicates extrinsic behavior through dopant (impurity) levels close to the valence band, similar to BaGe 8 As 14 and related compounds. , Hall effect data at 300 K (Figure S7, Supporting Information) reveal a p-type nature of RbGe 7 As 15 and CsGe 7 As 15 with carrier concentrations of 1.3 × 10 20 cm –3 and 8.2 × 10 19 cm –3 and mobilities μ of 5.8 and 21 cm 2 V –1 s –1 , respectively, similar to those of BaGe 8 As 14 with p = 2.3 × 10 20 cm –3 and μ = 2 cm 2 V –1 s –1 …”