First-shell Coordination Research Articles

Hydration of the halide ions in certain organic solvents

The amount of water co-extracted by the halide anions into several solvents has been determined. The order was always Cl − > Br − > I −, and at high organic-phase salt concentrations, the hydration numbers increased with increasing concentration, apparently paralleling the formation of ion pairs and higher ion aggregates. In nitrobenzene the lower, limiting values are 3·3, 1·8, and 1·0 moles of water per anion for Cl −, Br −, and I −, respectively. With dichloroethane as solvent, and more particularly with chloroform, solvation of the anion by the (weakly) acid proton of the diluent replaces part of the hydration, and the hydration number observed decreases markedly. For a number of reasons, the hydration numbers observed are lower limits to the first-shell hydration or coordination number of the anion.