Exploring the self-assembling ability of cyclometallated Rh(III) complexes with different N,N-chelating ligands in water.

Ionic [Rh(ppy)2(N^N)]OOCCH3 octahedral coordination complexes (Rh_bpy and Rh_phen; ppy = phenylpyridine; N^N = 2,2'-bipyridine, bpy; phenanthroline, phen) are synthesized, and their behaviour in water is investigated in comparison with previously reported structurally analogous Ir(III) complexes. Single-crystal X-ray analysis of both Rh(III) complexes reveals significant structural differences upon the substitution of the N^N chelating ligand, substantially affecting their supramolecular organizations. The observed difference in the ability to self-assemble in water between Rh_bpy and Rh_phen highlights the essential role of the different N^N chelating ligands in the modulation of intermolecular interactions, leading to distinct hierarchical network structures. While the Rh_bpy complex self-assembles in water at a relatively low concentration (from 1.9% w/w), giving rise to a mesophase with a lyotropic chromonic-like characteristic nematic texture, Rh_phen, due to its limited dissolution in water, does not reach the concentrations required to form homogeneous mesophases. The lyotropic-like phase of Rh_bpy is characterised in detail by polarized optical microscopy (POM) observations, wide-angle X-ray scattering (WAXS) and small-angle neutron scattering (SANS). These features contrast sharply with what has already been reported for structurally analogous Ir(III) complexes, where a completely different behaviour in water is observed upon changing the ligand while keeping the metal ion constant.