The crystal structure of the Cs 2 BX 6 (B = Sn, Ti; X = Cl, Br, I) family of vacancyordered perovskites is shown in Fig. . The low structural dimensionality of this family is expected to produce similar behavior to the corresponding [BX 6 ] 2 -molecular salts. One consequence of this 'molecular' crystal structure is the possibility for intermolecular interactions, such as London dispersion, between the localized octahedra. Table corroborates this hypothesis, showing contraction of the calculated lattice parameters upon inclusion of dispersion corrections in the model, demonstrating the presence of important van der Waals Figure : a. Crystal structure of Cs 2 BX 6 vacancy-ordered perovskites, in the conventional cubic unit cell (space group: F m3m). Cs atoms in green, M-cations in blue, and halide anions (X) in purple.