Figure 2.

Octahedral (Oct) motifs of ternary and quaternary Cu–Ag–Bi–I compounds.^1,2,18−22 (a) The spinel Oct motif of x ≥ 0 Ag_1–3xBi_1+xI₄ and CuBiI₄ consists of a 3D edge-sharing Oct motif present in spinel (Figure S12) with half of the Oct interstitials occupied. Using the transformation matrix shown, it can be represented in a trigonal unit cell where it can be considered as alternating between layers of 75% and 25% Oct interstitials occupied, maintaining the overall half Oct site occupancy. The reduction in symmetry splits the octahedra into two different sites (depicted by the purple and yellow colors). This representation is necessary to refine the rhombohedral strain of CuAgBiI₅. (b) The 2D CdCl₂ Oct motif consists of alternating between layers of full Oct interstitial occupancy and vacant layers, giving overall half Oct interstitial occupancy. (c) The NaVO₂ Oct motif consists of every possible Oct interstitial being occupied, with layered ordering. The layered ordering means that the layers alternate between two different Oct sites. Unit cells are drawn with solid black lines.