A combined thermal scanning-X-ray diffraction (XRD) approach was performed for the WBr6-P system to detect and analyze phases in this system, including metal-rich phases generated with increasing amounts of elemental (red) phosphorus under partial PBr3 release. Phases were characterized by powder XRD. A black crystalline powder of W-4(PBr)Br-10 was obtained after reduction of WBr6 with elemental phosphorus at 450 degrees 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(mu(4)-PBr)Br6i)Br-8/2(a-a) arrangement via outer bromide ligands. The mu(4)-capping bromophosphinidene ligand was verified by solid-state magic-angle spinning P-31 NMR spectroscopy.