Characterization of the intermediates formed in the reaction of Al atoms with H2O, H2S and H2Se by EPR spectroscopy

Abstract

Ground-state Al atoms have been reacted with H₂O, D₂O, H₂S, D₂S and H₂Se in an adamantane matrix in a rotating cryostat at 77 K. EPR spectra demonstrate that Al atoms are inserted into these Group 16 hydrides and deuterides to give the thermally unstable species, HAlOH, DAlOD, HAlSH, DAlSD and HAlSeH. These species have large almost isotropic Al and H hyperfine interactions (hfi) of 911–984 and 134–286 MHz, respectively, and g factors of ca. 1.999. In addition, HAlSH and HAlSeH have a small H hfi of 14 and 20 MHz, respectively. Theoretical calculations show that these novel aluminium complexes have bent geometries with most of the unpaired spin located on the HAl function. While the reactions with H₂O and D₂O form primarily the insertion product, H₂S and H₂Se also produce a number of mononuclear aluminium species tentatively assigned to Al(XH)₂ and Al(XH)₂(H₂X)_n, where X = S or Se and n= 1 or 2. The Al hfi for these complexes range from 830 to 1218 MHz. Finally, in the case of the reaction of Al atoms with H₂S, the tight ion pair Al⁺HSSH^–, with the parameters a_Al= 21 MHz and a_H(2)= 21 MHz, is generated. The results obtained from the Al atom–D₂S reaction support this assignment. No evidence has been obtained for the reaction of ground-state Ga atoms with H₂O to give HGaOH. H₂S, on the other hand, gives Ga⁺HSSH^– and there is tentative evidence for the formation of HGaSH and Ga(H₂S)₄.