New electronic parameter for ligands’ donor strengths

10 Dec 2014. NUS professor has developed a new and unified electronic parameter for ligands’ donor strengths.

A team led by Prof HUYNH Han Vinh from the Department of Chemistry in NUS has discovered that Ligand donor strengths can be easily determined by accurate 13C NMR spectroscopy as compared to the traditionally used carbonyl-based IR methodologies.

The sterics of a ligand can be intuitively estimated, but the determination of its net electron donating ability is not trivial. By comparing 13Ccarbene NMR signals (see Figure) in trans-[PdBr2(iPr2-bimy)(L)] and [PdBr(iPr2-bimy)(L-L)] complexes a new and unified electronic parameter has been developed for monodentate (L) and bidentate (L-L) ligands, which is non-destructive, safer and more accurate compared to the traditional carbonyl-based IR spectroscopic methodologies.  

Preparation of traditional complex probes requires toxic materials. In addition, small changes in the ligand structure could not be resolved due to the lower sensitivity of IR spectroscopy. With the new electronic parameter the influence of subtle and remote changes in the ligand structure can be detected in a simple way. This allows for electronic tuning in metal complexes on a finer level, possibly improving and impacting their applications in areas such as catalysis or photoluminescent materials. With a more in-depth knowledge of the electronic influence, tailor-made complexes can be designed to better suit their application.


The figure shows the unified donor strength scales of monodentate and bidentate ligands. The more donating the ligand, the more downfield (larger ppm) the 13Ccarbene signal. [Image credit: HUYNH Han Vinh]



1. Teng Q, Huynh HV “Determining the Electron-Donating Properties of Bidentate Ligands by 13C NMR Spectroscopy” Inorg. Chem. 53 (2014) 10964.

2. Huynh HV, Han Y, Jothibasu R, Yang JA. “13C NMR Spectroscopic Determination of Ligand Donor Strengths using N-Heterocyclic Carbene Complexes of Palladium(II)” Organometallics 28 (2009) 5395.