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Photochemical generation and chemical reactivity of hydridopentaaquochromium(III) ions

Journal Article · · Inorg. Chem.; (United States)
DOI:https://doi.org/10.1021/ic50226a072· OSTI ID:5646089
The complex (H/sub 2/O)/sub 5/CrH/sup 2 +/ was prepared by UV flash photolysis of aqueous chromium(II) perchlorate solutions in dilute perchloric acid. This species /sup 1//sub max/ = 385 +- 5 nm) has a short lifetime owing to its rapid reaction with H/sub 3/O/sup +/ (k = 1.0 +- 0.1) x 10/sup 4/ M/sup -1/ s/sup -1/ at 26/sup 0/C and ..mu.. = 0.20 M) to evolve hydrogen. The rate constant was studied as a function of ionic strength, confirming the 2+ charge, and a ..mu.. = 0.20 M as a function of temperature, providing the activation parameters ..delta..H double dagger = 26.4 +- 0.9 kJ mol/sup -1/, ..delta..S double dagger = -79.9 +- 2.9 J mol/sup -1/ K/sup -1/. The acidolysis of CrH/sup 2 +/ occurs 2 x 10/sup 6/ times more rapidly than that of methylpentaaquochromium(III) ion, (H/sub 2/O)/sub 5/CrCH/sub 3//sup 2 +/. Protonolysis of CrH/sup 2 +/ in H/sub 3/O/sup +/ as compared to CrD/sup 2 +/ in D/sub 3/O/sup +/ shows an appreciable kinetic isotope effect (k/sub H//k/sub D/ = 4.8) as does the protonolysis of CrCH/sub 3//sup 2 +/ in the same two solvents (k/sub H//k/sub D/ = 6.3). The mechanism in both cases involves O . H bond breaking more so than chromium-hydrogen (or chromium-carbon) cleavage.
Research Organization:
Iowa State Univ., Ames
DOE Contract Number:
W-7405-ENG-82
OSTI ID:
5646089
Journal Information:
Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 20:12; ISSN INOCA
Country of Publication:
United States
Language:
English