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The yellow (CH 3 NH 3 ) 4 PbI 6 •2H 2 O(P2 1 /n, a = 10.421(3) Å, b = 11.334(2) Å, c = 10.668(2) Å, β = 91.73(2)°, Z = 2) contains isolated PbI 6 4− octahedra, CH 3 NH 3 + cations of two types and H 2 O molecules. The cations and the water molecules are hydrogen-bonded to form Formula: see text units arranged in centrosymmtric Formula: see text pairs; the centres of these composite units and the Pb atoms form a distorted NaCl-type lattice. The Pb—I bond lengths in the PbI 6 4− anions are compared with those in Pb(II)I 6 ε complexes containing shared I atoms and the effect of the sharing on the bond lengths is discussed. A scheme is proposed for the extensive three-dimensional hydrogen bonding in the structure.
Vincent et al. (1987) studied this question.