Nitrosodisulphonates and hydroxylamine-N,N-disulphonates. V. A potassium salt of hydroxylamine-N,N-disulphonic acid with a displacive superlattice structure

Abstract

The structure of the potassium salt of hydroxylamine-N,N-disulphonate, with the formula K5HN2S4O14•H2O, has been determined by X-ray diffraction. The crystals are triclinic, a = 14.011(6), b = 16.118(9), c = 11.867(6) Å, α = 103.28(6), β = 106.76(3), γ = 86.38(3)°, [Formula: see text] with Z = 6. The integrated intensities of 8694 independent reflections were measured on a four-circle diffractometer, 5236 of which were used in the refinement to give a final least-squares weighted residual of 0.107 and a conventional R factor of 0.081.The structure forms a six-fold derivative lattice, which arises by small displacements (ca. 0.2 Å) of the atom positions from an average structure which is triclinic with Z = 1. This results in three very short H bonds, average length 2.46 Å, which link the three independent anion-dimers, being symmetry-free in this structure. Other bond lengths and angles in the anions are very similar to those in the Rb salt. The K+ ions show 8, 9, and 10 coordination, in a number of different polyhedral types. The three independent water molecules are each coordinated to three totally distinct K+ ions, and are linked to the anions by weak H bonds. The structural complexity may be explained in terms of a Lewis acid–base "mismatch" of the cations and anions present.