The ·AlH –3 anion and related species in γ-irradiated aluminium hydrides. An electron spin resonance study

Abstract

Exposure of tetrabutylammonium aluminium hydride to ⁶⁰Co γ-rays at 77 K gave two species exhibiting large, nearly isotropic, hyperfine coupling to ²⁷Al. One species, similar to that previously thought to be ·AlH^–₃ in irradiated lithium aluminium hydride, is now assigned to a hydroxylated impurity anion. The other, which exhibited hyperfine coupling to three equivalent protons, is clearly authentic ·AlH^–₃. This species was rotating in the solid matrix at 77 K, but anisotropic parameters were extracted from the spectra at 4 K. The results confirm the pyramidal character of ·AlH^–₃, but the estimated 3s population of 15.6% is almost equal to that for the isoelectronic radical ·SiH₃(15.0%)(P. J. Krusic and J. K. Kochi, J. Am. Chem. Soc., 1969, 91, 3938; S. W. Bennett, C. Eaborn, A. Hudson, R. A. Jackson and K. D. J. Root, J. Chem. Soc. A, 1970, 348) rather than being greater, as had been previously postulated.