Heteroleptic trivalent chromium in coordination chemistry: Novel building blocks for addressing old challenges in multimetallic luminescent complexes
Juan‐Ramón Jiménez, Benjamin Doistau, Maxime Poncet, Claude Piguet
Abstract
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.