A combined thermal scanning-X-ray diffraction (XRD) approach was performed for the WBr(6)-P system to detect and analyze phases in this system, including metal-rich phases generated with increasing amounts of elemental (red) phosphorus under partial PBr(3) release. Phases were characterized by powder XRD. A black crystalline powder of W(4)(PBr)Br(10) was obtained after reduction of WBr(6) with elemental phosphorus at 450 °C. The crystal structure of the new compound was found to be isotypic with the structure of W(4)(PCl)Cl(10) on the basis of powder XRD data. The structure of W(4)(PBr)Br(10) is represented by a cyclobutadiene-like tetranuclear tungsten cluster interconnected into a layered (W(4)(μ(4)-PBr)Br(6)(i))Br(8)/(2)(a-a) arrangement via outer bromide ligands. The μ(4)-capping bromophosphinidene ligand was verified by solid-state magic-angle spinning (31)P NMR spectroscopy.