Crystal structure of thallium(I)L-ascorbate

Abstract

Crystals of the title compound are orthorhombic, space group P2₁2₁2₁, a= 10·883(7), b= 18·598(6). c= 8·066(3)Å. There are two molecules per asymmetric unit, related by a pseudo-two-fold axis parallel with the a axis. The two thallium(I) ions are 4·05 Å apart and bridged by oxygen atoms. Co-ordination about the cations is typically asymmetric, involving only three and four oxygen atoms (from four anions); in each case the oxygens are grouped on one side of the thallium ion. Each ascorbate anion comprises a γ-lactone ring and an acyclic side-chain at C(4)(of the hexose skeleton); the anions are very similar and resemble the anion of sodium ascorbate. The lactone rings both appear planar. The O(3) atoms, each only 2·58 Å from a thallium ion, are pushed considerably out of the ring planes. The conformations about the C(6) atoms form the major difference between the anions; these conformations probably result from molecular packing and a complicated hydrogen-bonding system which, with the Tl ⋯ O interactions, holds the crystal as a lattice polymer.

The structure was solved from diffractometer data by the heavy-atom method, and refined by block-diagonal, and finally full-matrix, least-squares methods to R0·076 for 1253 reflections. The absolute configuration was assigned by comparison with L-ascorbic acid, the precursor of this compound.