Quaternary Tellurides with Different Valent Ge Centers: Cs₂Ge₃M₆Te₁₄ (M = Ga, In)

New quaternary tellurides, Cs₂Ge₃M₆Te₁₄ (M = Ga, In), were discovered by solid-state reactions. These compounds crystallize in space group <i>P</i>3<i>m̅</i>l (No. 164), with <i>a</i> = <i>b</i> = 8.2475(2) Å, <i>c</i> = 14.2734(8) Å, and <i>V</i> = 840.82(6) ų (<i>Z</i> = 1) for Cs₂Ge₃Ga₆Te₁₄ (<b>1</b>) and <i>a</i> = <i>b</i> = 8.5404(2) Å, <i>c</i> = 14.6766(8) Å, and <i>V</i> = 927.07(6) ų (<i>Z</i> = 1) for Cs₂Ge₃In₆Te₁₄ (<b>2</b>). The remarkable structural feature is the novel three-dimensional [Ge₃M₆Te₁₄]^2– anionic framework made by condensed In₆Te₁₄ (or Ga₆Te₁₄) layers that are connected alternately by dimeric Ge³⁺₂Te₆ units and Ge²⁺Te₆ octahedra along the <i>c</i> direction. The presence of Ge centers with different oxidation states is also supported by the results of the electron localization function calculation and X-ray photoelectron spectroscopy measurement