Pressure-dependent aquation of the Tris(2,2'-bipyridyl)iron(II) cation

The aquation of Fe(bpy)32+ (bpy = 2,2'-bipyridyl) was studied in aqueous hydrochloric acid at a range of pressures between 1 and 2070 bar. Activation volumes (ΔV‡) in 1.0 M HCl (+ 12.3 cm3 mol-1), 0.01 M HCl (+14.8cm3 mol-1), 1.0 M DCl (+13.3 cm3 mol-1) and 0.01 M DCl (+16.3 cm3 mol-1) were determined. A mechanism involving a significant positive contribution to ΔV‡ arising from a low-spin ↔ high-spin preequilibrium is proposed. The minor effect of the deuterium solvent isotope on ΔV‡ is consistent with this proposal.