High Resolution and Solid State NMR Investigations of Subvalent Gallium Compounds

The 71Ga NMR spectra of Ga[GaX4] melts and of solutions in benzene and other hydrocarbons show discrete sharp Ga1 and broad GaIII resonances. In the light of recent structure determinations, the solution Ga1 signals must be attributed to bis(arene)Ga+ complexes in which the gallium atom is n6-bonded to the hydrocarbons. The low line widths and strong high field shifts are attributed to an almost spherical shielding of the metal nucleus by the 4 s2 electrons. Solid state 69Ga and 71 Ga NMR spectra of Ga[GaCl4] crystalline powder show only Ga1 resonances. While the 71 Ga1 line is rather narrow, the 69Gal line has a complex fine structure. Consistent with the crystal structure of Ga[GaCl4], the Ga1 ion is calculated to have a very low quadrupole coupling constant e2qQ/h = 1.7 ± 0.1 MHz and an asymmetry parameter n = 0.44. Experimental and simulated line shapes (using literature models) are in satisfactory agreement, implying that the 69Ga signal splitting is due to second order quadrupolar effects for the central m = + 1/2 ⇋– 1/2 transition. The analogous splitting of the 71Ga NMR line is too small to be detected.