Chiral two-dimensional (2D) halide perovskites are formed by embedding chiral organic cations in a perovskite crystal structure. The chirality arises from distortions of the 2D metal halide layers induced by the packing of these organic cations. Sn-based octahedra spontaneously distort, but it remains unclear whether this intrinsic structural instability enhances the chirality. We investigate the effect of the metal cation on structural and phonon chirality in ${\text{MBA}}_2{\text{Sn}}_x{\text{Pb}}_{1-x}{\text{I}}_4$ (x = 0, 1/2, and 1). Incorporating Sn does distort the metal halide octehedra, yet it only has a minor impact on the structural chirality. In contrast, the phonons in ${\mathrm{MBA}}_2{\mathrm{SnI}}_4$ are substantially more chiral than in ${\mathrm{MBA}}_2{\mathrm{PbI}}_4$, especially the in-plane acoustic modes. However, this enhanced phonon chirality does not lead to a generation of a larger angular momentum under a temperature gradient, because the contributions of different chiral phonons tend to compensate one another.

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• Phonons
• Chiral symmetry
• Molecular dynamics