2H Quadrupolar Coupling Constant: A Spectroscopic Ruler for Transition Metal–Hydride Bond Distances in Molecular and Surface Sites

Transition-metal hydrides (TMHs) find numerous applications across fields, from catalysis to H2 storage. Yet, determining the structure of TMHs can remain a challenge, as hydrogen is difficult to detect by X-ray based or classical spectroscopic techniques. Considering that deuterium isotope (D) is a quadrupolar nucleus (I = 1) and that a quadrupolar coupling constant (CQ) depends on the distance between D and its bonding partner E (dED), we evaluate this trend across molecularly-defined transition-metal deuterides (TMDs) through a systematic investigation across TM block elements using both computations and experiments. We show that the M–D bond distance (dMD) in [Å] correlates with the CQ values in [kHz] as dMD = 7.83(CQ + 28.7)-1/3 - independently from the nature of the TM - with an accuracy > 0.04-0.08 Å. Based on experimental CQ values measured by 2H solid-state NMR, this simple correlation is then used to obtain the M-D bond distances in two silica-supported TMDs (M = Zr and Ir), notable heterogeneous catalysts, representing early and late TMDs, where evaluating M-D bond distances by other means is very challenging. Considering the ease of measurement, this method is readily applicable to a large range of diamagnetic terminal M–Ds, from molecular to surface sites, making 2H NMR a method of choice to measure TMDs bond distances.