Trensal (2,2’,2’’-tris(salicylideneimino)triethylamine) and its derivatives have a broad use as a heptadentate chelator that can encapsulate a metal leaving little or no open coordination sites depending on the substituents on the ligand as well as the size of the metal. In lanthanides and actinides, we can often see it forming a pocket that allows for only one other ligand to bind. In some cases, these compounds can form bridged systems that could possibly exhibit unusual interactions when metal – metal distances are close to the Hill limit (~3.4 Å). This limit is set at 2 times the distance of the valence 4f or 5f orbitals. These close metal – metal distances could result in greater overlap of the valence f orbitals. Other tripodal tren-type ligands with softer donor functional groups present such as N-Heterocyclic Carbenes (NHC’s) may have similar interactions and coordination environments in multidentate systems with one area for coordination. Whether these ligands push the Hill limit or not, they are of importance because of their interesting spectroscopic properties as well as providing further elucidation of the complexities of lanthanide and actinide bonding.

Interactions of trensals and other soft donor ligands with heavy metals

ACS Spring 2022

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