PGSE diffusion NMR : an emerging technique for inorganic/organometallic chemists

For a long time, X-ray and mass spectroscopic methods have been the techniques of choice for determining the size of organometallic/coordination complexes. However, the chemistry community has awoken to the recent advances in NMR, among which pulsed field gradient spin-echo (PGSE) diffusion NMR is attracting considerable interest.[1–3] PGSE is a powerful technique for probing intermolecular interactions in solution. Importantly, NMR is a non-invasive technique that does not perturb the thermodynamics of the system. PGSE diffusion NMR measurements were introduced about 40 years ago and the technique is a promising addition to the field of inorganic chemistry. This has been possible because of the use of multinuclear PGSE studies for obtaining the translational diffusion coefficients (D) of various nuclei. In addition, the range of accessibility of diffusion coefficients using current commercial equipment is from 10-9 down to ~10-11 m2 s-1 with the magnetic gradient strengths typically found on high resolution probes. With specialized probes, it is possible to extend this to 10-15 m2 s-1 under favourable conditions. The theory and procedures for performing the PGSE diffusion NMR experiment has been explained in detail elsewhere.[2–4] The present article highlights some of the latest applications of the PGSE diffusion NMR technique to organometallic chemistry