Heteroleptic trivalent chromium in coordination chemistry: Novel building blocks for addressing old challenges in multimetallic luminescent complexes

• Published in: Coordination chemistry reviews 2021-05, Vol.434, p.213750, Article 213750
• Main Authors: Jiménez, Juan-Ramón, Doistau, Benjamin, Poncet, Maxime, Piguet, Claude
• Format: Article
• Language: English
• Subjects: Chromium; Heteroleptic complexes; Kinetic inertness; NIR emission; Sensitizers
• ISSN: 0010-8545; 1873-3840
• DOI: 10.1016/j.ccr.2020.213750

Tailored heteroleptic trivalent chromium complexes combine kinetic inertness and structural control with tuneable photophysical properties, all aspects which are crucial for the design of a next gereneration of cheap (supra)molecular light-converting assemblies and devices. [Display omitted] •Photoactive Cr(III) complexes as an alternative to precious Ru(II) complexes.•Lability-induced Cr(III) complexes as precursors for heteroleptic complexes.•Inert Cr(III)N6 complexes might be exploited in metallo-supramolecular structures.•Cr(III)N6 sensitizers can be programmed for providing long NIR excited state lifetimes. Although less famous than low-spin trivalent cobalt found in [CoIII(NH3)6−xClx]Cl3−x (x ≤ 3), which was exploited by Alfred Werner during the early part of the 20th century for establishing the basic rules of coordination chemistry, related trivalent chromium complexes exhibit comparable kinetic inertness, a rare property along the 3d-transition series. The associated slow isomerisation processes are compatible with the isolation of well-defined heteroleptic complexes. Some subtle energetic differences between CrIII-X (X = halide, pseudo-halide, cyanide, solvent) and Cr-N bonds can be exploited for preparing stable and inert cis/trans-[Cr(N ∩ N)2X2]+ and fac/mer-[Cr(N ∩ N ∩ N)X3] primary heteroleptic complexes incorporating multidentate nitrogen-containing chelate ligands. The use of these building blocks within the frame of the ‘complex-as-ligand’ strategy, or via the labilization of the remaining Cr-X bonds pave the way for the design of discrete polymetallic assemblies in which the photophysically appealing [CrIIIN6] chromophores could find applications as functional light-converting devices.