Crystal structure of potassium nitrilotrisulphonate dihydrate

Abstract

The crystal structure of potassium niltrilotrisulphonate dihydrate, H₄K₃NO₁₁S₃, has been determined by use of three-dimensional equi-inclination Weissenberg X-ray diffraction data with 805 visually estimated reflections. There are four molecules in the orthorhombic unit cell, space group P_nma(D_2h¹⁶), with dimensions, a= 11·189(1), b= 5·776(7), c= 18·06(1)Å. The structure was refined by least-squares calculations to R 0·12. Each molecule is on a crystallographic mirror plane, with two of the oxygen atoms for each SO₃ group situated above and below this plane. The anion approximates to C_3h symmetry, with a planar NS₃ skelton [N–S, 1·71(2); S–O, 1·44(2)Å S–N–O, 120(1); O–S–O, 114(1)°]. The potassium atoms are surrounded by nine or ten oxygen atoms with K–O distances ranging from 2·6–3·2 Å Oxygen atoms of the water molecules are at least 2·8 Å from either the potassium atoms or the nitrilotrisulphonate anion. An explanation is offered for the stereochemistry of the class of compounds A(BC₃)₃.