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Taming 2,2′-biimidazole ligands in trivalent chromium complexes

Published inDalton transactions, vol. 53, no. 38, p. 15801-15814
Publication date2024-10-14
First online date2024-07-06
Abstract

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.

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Citation (ISO format)
CHONG, Julien et al. Taming 2,2′-biimidazole ligands in trivalent chromium complexes. In: Dalton transactions, 2024, vol. 53, n° 38, p. 15801–15814. doi: 10.1039/d4dt01608d
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Additional URL for this publicationhttps://xlink.rsc.org/?DOI=D4DT01608D
Journal ISSN1477-9226
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