The structure of the title compound, C16H40N4P+. Br-.0.5H(2)O or [P{N(C2H5)
(2)}(4)]Br .0.5H(2)O, 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) Angstrom. The N atoms are approximately planar. The water mol
ecules form cyclic hydrogen-bonded [(H2O)(2)Br-2](2-) units about inversion
centers, with O . . . Br distances in the range 3.425 (2)- 3.611 (3) Angst
rom.