Structural Differences between the Alkali Imidodisulphates

Abstract

IT has long been known from goniometric measurements¹ that there are morphological similarities between ammonium and potassium imidodisulphates (or iminodisulphonates), NH(SO₃NH₄)₂ and NH(SO₃K)₂. The crystal structure of the potassium salt², which has recently been refined³, conforms accurately to the space-group C 2/c. Preliminary X-ray examination of single crystals at room temperature revealed⁴ that ammonium imidodisulphate differs somewhat in structure from the potassium salt in that its true unit cell has a b-axis three times as long (3 × 7.74 = 23.2 Å) as a pseudo-cell isomorphous with the potassium salt. Rubidium imidodisulphate appears to have a five-fold superlattice since, on b-axis photographs, a few reflexions can be seen on up to four additional weak layer-lines between adjacent strong layer-lines. In both salts, reflexions on the extra layer-lines are of very low intensity. We have investigated these structural irregularities by means of X-ray diffraction and broad-line nuclear-magnetic-resonance spectroscopy.