| Abstract
| - Sn19.3Cu4.7As22I8, a new clathrate-I compound with a cationic host framework containing transition metals, has beensynthesized, and its crystal structure has been determined. It crystallizes in the cubic space group Pm3̄n with aunit cell parameter a = 11.1736(3) Å and Z = 1 (R = 0.031 for 329 independent reflections and 22 variables).Tin, copper, and arsenic form the cationic clathrate framework hosting the guest iodine anions in cages of twodifferent shapes. Sn19.3Cu4.7As22I8 does not contain vacancies in the framework but reveals three partially occupiedpositions of the metal atoms, leading to the formation of Sn−Sn and Sn−Cu bonds that differ in length. The 119SnMössbauer spectrum confirms the local environment of tin atoms. The hyperfine constants obtained from theMössbauer spectra for different cationic tin clathrates are discussed. Electron diffraction and electron microscopyreveal that the splitting affects the short-range ordering but does not lead to a superstructure. Though containinga transition metal, Sn19.3Cu4.7As22I8 is diamagnetic, and its composition corresponds to the Zintl formalism.
- A short-range ordering, which does not lead to any detectable superstructure of the type-I clathrate, is observed in Sn19.3Cu4.7As22I8, the first clathrate compound containing transition-metal atoms in the cationic framework. The local ordering within the clathrate framework results in the splitting of the 24-fold position into three partially occupied sites caused by the difference in the homonuclear Sn−Sn and notably polar Sn−Cu bonds.
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