Trimeric Phenylphosphonitrile Bromides: (1,3,5-Tribromo-L,3,5-Triphenylcyclotriphosphazatrienes; 2,4,6-Tribromo-2,4,6-Triphenyl-2,2,4,4,6,6-Hexahydro-1,3,5,2,4,6-Triazatriphosphorines )