Modulating the Dimensionality and Optical Properties of OMHs via Organic Cation Rearrangement

Organic-metal halides (OMHs) have emerged as a versatile class of materials, where the integration of organic cations with diverse electronic properties provides structural tunability that surpasses traditional all-inorganic halides. Despite their potential, the rational design of OMH crystal structures remains a significant challenge, with current synthetic strategies predominantly relying on stochastic trial-and-error methods. In particular, the fundamental mechanisms by which organic cations dictate structural dimensionality are not yet fully understood. Ten organic-metal halides with 2D, 1D, and 0D architectures were synthesized using benzene-ring diammonium cation templates bearing subtly varied side groups. We demonstrate that the structural dimensionality is governed by a synergistic interplay of steric hindrance and multidirectional hydrogen bonding. A larger cation rearrangement volume sterically isolates Pb–Br octahedral units, hindering their connectivity, while multidirectional hydrogen bonds anchor bromine atoms at multiple sites, effectively cleaving the inorganic framework. This synergy promotes one-dimensional chain-like configurations. This work provides a new theoretical framework and molecular engineering strategy for the predictable design of low-dimensional organic-metal halides.