Effect of counterions on the ribbonlike supramolecular assembly formation of dinuclear metal complexes in the lyotropic mesophase

The effect of counterions on the formation of the ribbonlike supramolecular assembly of a dinuclear metal complex in the lyotropic mesophase has been examined by optical microscopy, cryo-transmission electron microscopy, atomic force microscopy, and X-ray diffraction. Potassium and ammonium salts of [Cr-2(L-tart(2)H)(phen)(2)](-) (tart = tartrate(IV-), phen = 1, 10-phenanthroline) in water display liquid crystals, where ribbonlike assemblies are formed like that of the sodium salt. Sheetlike assemblies are found in dilute solutions of sodium, potassium, and ammonium salts. On the other hand, aqueous solutions of [Co(en)(3)](3+) (en = ethylenediamine) salts do not display liquid crystals because of the nonrigid character of the ribbons. The [Co(en)(3)](3+) salts form sheets and ribbonlike assemblies in the same solution. The ribbons gather like strings or roll spirally. The characteristic assembly formation of [Co(en)(3)](3+) salts may originate in the bulky structure of [Co(en)(3)](3+).