The structures of [MPh4][BPh4], M = P, As and Sb, crystallize in a sup
erstructure (I (4) over bar, Z' = 1/2) of the P (4) over bar 2(1)c, Z'
= 1/4, structure known for MPh4, M = C, Si, Ge, Sn and Pb. The arrang
ement of the ions is the same as for CaWO4 (scheelite; I4(1)/a, Z' = 1
/4), which is typical of many other ionic XYO4 structures. Crystals of
[MPh4][BPh4] turn a pinkish amber when exposed to UV light; ESR spect
ra confirm that free radicals are generated.