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Getting Ready for the Hydrogen Evolution Reaction: The Infrared Spectrum of Hydrated Aluminum Hydride-Hydroxide HAlOH⁺ (H₂ O)_n-1 , n=9-14.

ABSTRACT: Hydrated singly charged aluminum ions eliminate molecular hydrogen in a size regime from 11 to 24 water molecules. Here we probe the structure of HAlOH⁺ (H₂ O)_n-1 , n=9-14, by infrared multiple photon spectroscopy in the region of 1400-2250 cm^-1 . Based on quantum chemical calculations, we assign the features at 1940 cm^-1 and 1850 cm^-1 to the Al-H stretch in five- and six-coordinate aluminum(III) complexes, respectively. Hydrogen bonding towards the hydride is observed, starting at n=12. The frequency of the Al-H stretch is very sensitive to the structure of the hydrogen bonding network, and the large number of isomers leads to significant broadening and red-shifting of the absorption of the hydrogen-bonded Al-H stretch. The hydride can even act as a double hydrogen bond acceptor, shifting the Al-H stretch to frequencies below those of the water bending mode. The onset of hydrogen bonding and disappearance of the free Al-H stretch coincides with the onset of hydrogen evolution.

SUBMITTER: Heller J

PROVIDER: S-EPMC8361745 | biostudies-literature |

REPOSITORIES: biostudies-literature

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