Taming 2,2’-biimidazole ligands in trivalent chromium complexes† Chong, Julien Benchohra, Amina Besnard, Céline Guénée, Laure Rosspeintner, Arnulf Cruz, Carlos M. Jiménez Gallego, Juan Ramón Piguet, Claude Complete or partial replacement of well-known five-membered chelating 2,2’-bipyridine (bipy) or 1,10- phenanthroline (phen) ligands with analogous didentate 2,2’-biimidazole (H2biim) provides novel perspectives for exploiting the latter pH-tuneable bridging unit for connecting inert trivalent chromium with cationic partners. The most simple homoleptic complex [Cr(H2biim)3]3+ and its stepwise deprotonated analogues are only poorly soluble in most solvents and their characterization is limited to some solidstate structures, in which the pseudo-octahedral [CrN6] units are found to be intermolecularly connected via peripheral N–H⋯X hydrogen bonds. Moreover, the associated high-energy stretching N–H vibrations drastically quench the targeted near infrared (NIR) CrIII-based phosphorescence, which makes these homoleptic building blocks incompatible with the design of molecular-based luminescent assemblies. Restricting the number of bound 2,2’-biimidazole ligands to a single unit in the challenging heteroleptic [Cr(phen)2(Hxbiim)](1+x)+ (x = 2–0) complexes overcomes the latter limitations and allows (i) the synthesis and characterization of these [CrN6] chromophores in the solid state and in solution, (ii) the stepwise and controlled deprotonation of the bound 2,2’-biimidazole ligand and (iii) the implementation of Cr-centered phosphorescence with energies, lifetimes and quantum yields adapted for using the latter chromophores as sensitizers in promising ‘complex-as-ligand’ strategies. 2024-09-02T08:51:48Z 2024-09-02T08:51:48Z 2024-07-06 journal article Chong, J. et. al. Dalton Trans., 2024. [https://doi.org/10.1039/D4DT01608D] https://hdl.handle.net/10481/93747 10.1039/D4DT01608D eng http://creativecommons.org/licenses/by/4.0/ open access Atribución 4.0 Internacional Royal Society of Chemistry