Ag₃SnCuP₁₀: [Ag₃Sn] tetrahedra embedded between adamantane-type [P₁₀] cages

Ag₃SnCuP₁₀ was synthesized from a stoichiometric mixture of copper, silver, tin, and red phosphorus, with SnI₄ added as a mineralization agent. Cubic Ag₃SnCuP₁₀, space group F43m (No. 216) with lattice parameter a = 10.503(1) Å and Z = 4, consisting of orientationally disordered [Ag₃Sn] heteroclusters and adamantane-type [P₁₀] cages, is one example in which structure determination was possible only by the combined use of diffraction and spectroscopic methods. An ideal 4-fold domain twin structure that results for a R3m model, featuring an ordered arrangement of the heteroclusters, cannot be differentiated from the F43m model by diffraction methods alone. After a detailed NMR spectroscopic examination using state of the art solid-state NMR techniques, we found the local environment around the [P₁₀] cages of the F43m model to be the correct description of the Ag₃SnCuP ₁₀ structure. A possible Cu/Ag or Ag/Sn disorder in the [Ag ₃Sn] heterocluster and within the copper substructure was excluded by Mössbauer spectroscopic investigations and NMR measurements.