Preparation, structure, and electronic properties of Ca₁₁MSb₉ (M = Al, Ga, In)

Two new Zintl compounds Ca₁₁MSb₉ (M = Al, Ga) and the Zintl compound Ca₁₁InSb₉ have been synthesized in quantitative yields by reacting the elements in an 11:1:9 ratio at high temperatures (850 and 1000°C). Low-temperature (130 K) single-cystal X-ray diffraction data show that the Ca₁₁GaSb₉ compound is orthorhombic, space group = Iba2, Z = 4, a = 11.805(3) Å, b = 12.463(3), c = 16.651(2) Å, R1 = 2.50%, wR2 = 5.22%, and is of the Ca11-InSb₉ structure type. Powder X-ray diffraction show that Ca₁₁AlSb₉ is also the Ca₁₁InSb₉ structure type. Room-temperature lattice parameters from powder diffraction data are as follows: Ca₁₁AlSb₉, a = 11.832(3) Å, b = 12.505(2) Å, c = 16.674(4) Å; Ca₁₁GaSb₉, a = 11.839-(2) Å, b = 12.536(3) Å, c = 16.716(1) Å; Ca₁₁InSb₉ a = 11.899(2) Å, b = 12.596(2) Å, c = 16.722(3) Å. Temperature-dependent resistivity measurements show that these materials are semiconducting.