On the crystal structure of the germanium-based cationic clathrates [Ge38.3Sb7.7]I7.44, [Ge38.1P7.9]I8, and [Ge30.5Sn7.7P7.75]I7.88

Compounds Ge_38.3Sb_7.7]I_7.44, Ge_38.1P_7.9]I₈, and Ge_30.5Sn_7.7P_7.75]I_7.88 with the clathrate type-I structure were synthesized. They crystallize in the cubic space group Pm`3]nPm\bar 3n with the unit cell parameter a = 10.8592(9), 10.4983(12), and 10.7210(10) ? (Z = 1), respectively. Their crystal structure represents the germanium(tin)-pnictogen framework, capturing the guest iodine anions in its cavities. All compounds have no vacancies in the host substructure; however, two of them show vacancies in the guest positions. The atomic distribution over the framework sites is of the most interest as it follows trends associated with the relative electronegativities of the atoms composing the framework. The results of the band structure calculations and application of the Zintl counting scheme are also discussed in relation to potential thermoelectric properties.