Crystal chemistry of tetraradial species. Part 2. Crystal structures of Et4NI, Ph4PBr•H2O, and Ph4PBr•2H2O

Abstract

The crystal structure of Et4NI [Formula: see text], a = 8.860(2) Å, c = 6.933(1) Å, Z = 2) has been redetermined and those of Ph4PBr•H2O ([Formula: see text], a = 10.005(3) Å, b = 10.659(2) Å, c = 10.697(4) Å, α = 102.61(2)°, β = 83.39(3)°, γ = 108.09(3)°, Z = 2) and Ph4PBr•2H2O (Pnma, a = 16.255(4) Å, b = 10.810(4) Å, c = 12.667(9) Å, Z = 4) have been determined for the first time. In the Et4NI structure Et4N+ cations in an extended S4 conformation and I− anions are arranged in a zincblende-type packing. The two hydrate structures are ionic and very similar. The anion in the monohydrate is a centrosymmetric cyclic dimer [Br2(OH2)2]2−; in the dihydrate the anion, which is an almost planar infinite [Br−(OH2)4/2]x chain 11b, appears to be of a novel type. If the H2O molecules are not considered, the ion packing in both hydrates may be regarded as of the anti-NiAs type. The ion packing in R4EX structures and the conformation of the Et4N+ ion in crystals are discussed in some detail.