Structure of barium perchlorate trihydrate

Ba(ClO4)2.3H2O, Mr=390.28, hexagonal, P63/m, a=7.277(2), c=9.656(1) A, V=442.9(1) A3, Z=2, F(000)=368, Dx=2.93 g cm-3, λ(Mo Kα=0.71069 A, T=295 K, μ=52.60 cm-1, 456 unique reflections, R=0.023. The barium atoms in this structure are coordinated by six water oxygens, O(3), at 2.919(1) A and by six perchlorate oxygens, O(2), at 3.026(2) A in a slightly distorted icosahedral arrangement, the average Ba-O separation thus being ≅ 2.97 A. The perchlorate ion just fails to have regular tetrahedral geometry within the experimental error, and has an average Cl-O bond length of 1.433(6) A. Consistent with hydrogen bonding delineated on the basis of least-squares-refined hydrogen-atom positions, each axial [O(1)] perchlorate oxygen is hydrogen bonded to three water molecules and each trigonal [O(2)] perchlorate oxygen is hydrogen bonded to two water molecules; thus each perchlorate ion is hydrogen bonded to nine water molecules. Conversely, each water molecule [O(3)] oxygen is hydrogen bonded to six perchlorate ions - to two through axial [O(1)] oxygens and to four through trigonal [O(2)] oxygens. (orig.)