Overcoming Synthetic Bottlenecks in Phosphorus Metal Halides via Temperature Gradients: Access to Previously Inaccessible Phases Including Cu2P3Br2

Abstract Low-dimensional phosphorus-based materials offer promising electronic properties but remain limited by instability or synthetic inaccessibility. Phosphorus metal halides (PMHs) provide an attractive alternative, combining air stability with quasi-one-dimensional phosphorus frameworks encapsulated by metal halide sheaths. However, the discovery of new PMHs has been severely constrained by the narrow and poorly controlled temperature windows required for their formation, leading to slow progress over several decades. Here, we demonstrate that temperature gradient engineering in a tube furnace enables phase-selective chemical vapor transport (CVT), overcoming a key limitation of the conventional uniform-temperature synthesis. Using this approach, we report the first synthesis and structural characterization of Cu2P3Br2, the long-sought bromide analogue of Cu2P3I2, alongside Cu12P20Br10, formed simultaneously within a single ampule. Spatially resolved crystallization along the temperature gradient reveals distinct formation zones, directly linking phase selection to local thermal conditions. Single-crystal X-ray diffraction confirms that Cu2P3Br2 adopts a quasi-one-dimensional phosphorus framework isotypic to that of Cu2P3I2. Device measurements show that both materials exhibit predominantly p-type semiconducting behavior with ambipolar features, highlighting their potential for use in electronic and optoelectronic applications. More broadly, this work establishes temperature-gradient-controlled CVT as a powerful and generalizable strategy for accessing previously inaccessible PMH phases. By enabling simultaneous phase exploration within a single reaction, this approach provides a scalable pathway for expanding the compositional and structural diversity of the phosphorus-based heterostructured nanomaterials.