Crystal and molecular structure of methyl α- d-galactopyranoside 4-(sodium sulphate) dihydrate

Abstract

The crystal and molecular structure of methyl α- d-galactopyranoside-4-(sodium sulphate) dihydrate has been determined by X-ray analysis at − 173°. The sugar ring has a distorted 4 C 1 chair conformation. The conformation of the CH 2OH group is gauche-trans and the bridging SO bond is eclipsed with the C-4H bond, which diminishes the steric repulsion of the sulphate group with the neighbouring CH 2OH and HO-3 groups. The sodium ions occupy special positions on two-fold axes and each is co-ordinated six-fold. The three independent oxygen atoms around Na-1 belong to two different sulphate oxygen atoms that are associated with two different sugar rings and O-3 of one of these rings. In the co-ordination of Na-2, the three independent oxygen atoms belong to one of the water molecules and one sulphate group. The co-ordination of Na-1 approaches ideal octahedral symmetry, whereas that of Na-2 is distorted appreciably. Both the co-ordination and hydrogen bonding result in a complex packing pattern in which the single hydrogen-bonded helix around the screw is axis involves the hydroxymethyl group and a water molecule, and is almost identical to the arrangement observed for methyl α- d-galactopyranoside monohydrate.