Anisotropic aggregation of a 1,10-phenanthroline dinuclear chromium(III) complex bridged by two L-tartrates in aqueous solution

Abstract

The aggregation of M[Cr₂(L-tart₂H)(phen)₂](phen = 1,10-phenanthroline, tart = tartrate, M = Na, K) in aqueous solution has been investigated by measuring ²³Na NMR of counterions, ²H NMR of water molecules, viscosity and electric conductivity. The physical properties of the solutions were compared with those for the bpy(= 2,2′-bipyridyl) analogue. In the solution of the phen complex the formation of large ion aggregates was observed even below 0.01 mol dm^–3 at 27 °C, in contrast to the bpy analogue where the solution behaves as a simple electrolyte solution up to concentrations of 0.2 mol dm^–3. The aggregate solutions were shown to form an anisotropic phase by ²³Na NMR measurements. ²³Na relaxation studies showed that the motion of the sodium counterions is strongly restricted by interaction with the aggregates. Measurements of deuterium relaxation of water molecules showed that there is extensive hydration of the ion aggregates at room temperature, while the extent is not so critical for the formation of the ion aggregates as is observed for the ²³Na relaxation rates.