Prospective Chalcohalide Perovskites: Pursuing the Synthesis of CsBiSCl2 Nanocrystals

Heavy pnictogen chalcohalides are often referred to as lead-free, perovskite-inspired materials. Despite theoretical predictions, incontrovertible experimental demonstrations of heavy pnictogen chalcohalides adopting a perovskite structure are lacking. Here we report our attempts to prepare CsBiSCl2 adopting a perovskite structure as colloidal nanocrystals. Synthesis of nanoscale materials can indeed rely on fast, non-equilibrium reactions and on large, eventually thermodynamically favorable surface energies, leading to the possibility of stabilizing kinetically-trapped or metastable phases. However, we obtained no CsBiSCl2, but a mixture of nanocrystals of secondary phases, namely Cs3BiCl6 submicrometric polyhedra, Bi2S3 nanoscopic rods, and Cs3Bi2Cl9 nanoscopic dots, whose low polydispersity enabled an effective separation via size/shape selective precipitation. This work confirms that heavy pnictogen chalcohalides are hardly prone to adopt a perovskite structure. Nevertheless, chemistry at the nanoscale offers multiple possibilities to overcoming phase segregation and pursuing the synthesis of prospective mixed anion compounds.