Refinement of the crystal structure of magnesium sulphate heptahydrate (epsomite) by neutron diffraction

Abstract

The crystal structure of orthorhombic MgSO₄,7H₂O has been refined anisotropically to a final R of 0·048 over 900 independent neutron reflexions from a synthetic crystal. For the positional parameters of the 14 crystallographically independent hydrogen atoms, estimated standard deviations are ca. 0·007 Å, double those for the other atoms. All hydrogen atoms (mean O–H 0·964 Å) are engaged in hydrogen bonds, ranging from 2·692(7) to 2·982(7)Å. The W(7) water molecule, unique in that it is not co-ordinated to the magnesium, is engaged in relatively weak [(2·820(7) and 2·903(7)Å] appreciably non-linear hydrogen bonds; it may be partially absent in water-deficient natural specimens. The assumption of coplanarity of water atoms and oxygen-acceptor atoms proves to be an unreliable guide to hydrogen positions.