Using 69/71Ga solid-state NMR and 127I NQR as probes to elucidate the composition of “GaI”

While the synthetic utility and reactivity of the so-called “GaI” species is reasonably well established, its exact composition remains unknown. Using primarily multinuclear magnetic resonance techniques (and supported with powder X-ray diffraction measurements), we offer some new insights into the composition of “GaI”. Using 127I nuclear quadrupole resonance (NQR) experiments, it is clearly demonstrated that gallium diiodide (GaI2) is a significant component of this material, while GaI3 is not. This finding is in contrast with a prior literature account, which noted that Ga2I3 (i.e., one equivalent of GaI3 per equivalent of Ga metal) was present in significant amounts. Additional solid-state nuclear magnetic resonance (SSNMR) experiments using the 69/71Ga probe nuclei in multiple magnetic fields clearly establish, via its diagnostic Knight-shifted resonance, the presence of Ga0 metal, which is in agreement with prior literature. Taken together, a composition may be tentatively offered: that “GaI” is, to a large extent, two equivalents of Ga0 metal with two equivalents of GaI2, where the latter is composed of Ga+ and GaI4- ions. This composition may be represented as [Ga0]2[Ga]+[GaI4]−.

Gallium-69/71 solid-state nuclear magnetic resonance and iodine-127 nuclear quadrupole resonance spectroscopies are used to provide insight into the structure and composition of Green’s synthetically useful “GaI” reagent.Figure optionsDownload as PowerPoint slideHighlights
► 69/71Ga solid-state NMR and 127I NQR provide new details on “GaI” composition.
► Clear presence of GaI2 is detected for the first time.
► Prior reports which detect gallium metal are confirmed.
► “GaI” appears to be stable over long periods of time, if stored properly.