Crystal structure of ammonium fluorosulphate

Abstract

Crystals of ammonium fluorosulphate, NH₄SO₃F, are orthorhombic, a= 8·972, b= 5·996, c= 7·542 Å, Z= 4, space group Pnma. The structure was determined with Cu-Kα scintillation counter data by comparison with the potassium salt, and refined by least-squares methods, the final R being 0·078 for 293 observed reflexions.

The observed dimensions of the fluorosulphate anion are intermediate between those expected for C_2v and C_3v symmetries, so that the anion appears to be partially disordered in the crystal (75% of one orientation, 25% of a second), in contrast to the potassium salt, where the anion arrangement is completely disordered. The partial ordering in the ammonium compound is probably the result of hydrogen bonding. The dimensions derived for the isolated (C_3v) fluorosulphate ion (standard deviations in parentheses) are: S–O 1·45(2), S–F 1·55(2)Å, O–S–O 113(1)°, and F–S–O 106(1)°.