Issue 2, 1990

Stereochemistry of tervalent aqua ions: low-temperature neutron diffraction structures of CsFe(SO4)2·12H2O and CsFe(SeO4)2·12H2O

Abstract

The structures of CsFe(SO4)2·12H2O and CsFe(SeO4)2·12H2O have been investigated by neutron diffraction at 15 K. Both alums crystallise in the cubic space group Pa3, Z= 4, with a= 12.354(6)Å for the sulphate and 12.593(10)Å for the selenate. The structures were refined using 802 [CsFe(SO4)2·12H2O] and 1 059 [CsFe(SeO4)2·12H2O] inequivalent reflections to give weighted R factors of 0.029 and 0.028 respectively. In agreement with prior X-ray crystallographic determinations, CsFe(SO4)2·12H2O gives the β alum modification whereas CsFe(SeO4)2·12H2O forms an α alum. The stereochemistry of water co-ordination to FeIII differs in the two alums, with the angle between the metal (III)–water bond and the plane of the co-ordinated water molecule being 0.6(10)° for the sulphate and 18.6(10)° for the selenate. This tilting of the plane of the co-ordinated water molecule is shown to be related to the alum type. The iron(III)–water bond distance shows some sensitivity to the tilt of the co-ordinated water molecule, lengthening from 1.994(1) to 2.002(1)Å as the plane of the water molecule is tilted by 18.6°. The sensitivity of the alum type to the size of the constituent ions, and to the stereochemistry of water co-ordination to the tervalent cation, is discussed in light of the hydrogen bonding in the alum structures.

Article information

Article type
Paper

J. Chem. Soc., Dalton Trans., 1990, 395-400

Stereochemistry of tervalent aqua ions: low-temperature neutron diffraction structures of CsFe(SO4)2·12H2O and CsFe(SeO4)2·12H2O

S. P. Best and J. B. Forsyth, J. Chem. Soc., Dalton Trans., 1990, 395 DOI: 10.1039/DT9900000395

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