Abstract: | The structure of the title compound, C16H40N4P+·Br?·0.5H2O or [P{N(C2H5)2}4]Br·0.5H2O, at 130 K has Z′ = 4 and is ionic, with Br not bonded to P. The P atoms are tetrahedral, with P—N distances in the range 1.628 (2)–1.6400 (19) Å. The N atoms are approximately planar. The water molecules form cyclic hydrogen‐bonded [(H2O)2Br2]2? units about inversion centers, with O?Br distances in the range 3.425 (2)–3.611 (3) Å. |