THE STRUCTURE OF (ND4)2CR(SO4)2.6D2O AT 4.3-K BY NEUTRON-DIFFRACTION

Di(H-4(2))ammonium hexa[(H-2(2))aqua]chromium(II) disulfate, [ND4]2[Cr(D2O)6](SO4)2, M(r) = 407.1, monoclinic, P2(1)/a, a = 9.488 (2), b = 12.816 (4), c = 6.097 (2) angstrom, beta = 107.11 (1)-degrees, V = 708.6 (7) angstrom 3, Z = 2, D(m) = 1.90 (1), D(x) = 1.91 g cm-3, neutron, lambda = 1.176 angstrom, mu = 0.255 cm-1, F(000) = 463 fm, T = 4.3 K, R(F) = 0.018 for 1018 unique reflections, deuteration 95.1 (3)% for ammonium, 94.2 (2)% for water. The structure is very similar to the hydrogen-bonded network in the other isomorphous ammonium Tutton salts studied at 4 K. The CrO6 octahedron has a large Jahn-Teller distortion with a tetragonal elongation of Cr...O(8) = 2.389 (1), Cr...O(7) = 2.080 (1), Cr...O(9) = 2.054 (1) angstrom. The cell parameters and CrO6-octahedron geometry are virtually the same as those found in the previous 84 K X-ray charge-density study on the hydrogenous salt.