Stabilization of coordinated carbonate in aqueous acidic solution: steric inhibition of protonation in Co(III) complexes containing chelated carbonate

Inorganic Chemistry
Sarah E CheyneAllan G Blackman

Abstract

The synthesis, characterization, X-ray crystal structures, and reactivity in aqueous acidic solution of the Co(III) carbonate complexes [Co(tpa)(O2CO)]ClO4.H2O, [Co(Me-tpa)(O2CO)]ClO4.0.5H2O, [Co(Me2-tpa)(O2CO)]ClO4.0.5H2O, and [Co(Me3-tpa)(O2CO)]ClO4 are reported (tpa = tris(2-pyridylmethyl)amine; Me-tpa, Me2-tpa, and Me3-tpa are derivatives of tpa containing one, two, and three 6-methylpyridyl rings, respectively). The complexes display very different spectroscopic and 59Co NMR properties, consistent with the decreasing ligand field strength of the tripodal amine ligands in the order tpa > Me-tpa > Me(2)-tpa > Me3-tpa. X-ray structural data show an increase in the average Co-N bond distances as the number of methyl groups on the tripodal amine ligand increases, and this is the result of steric interactions between the methyl groups and the carbonate ligand and between the methyl groups themselves. Rate data for the acid hydrolysis of [Co(tpa)(O2CO)]+ (I = 1.0 M (NaClO4), 25.0 degrees C) over the [HClO4] range of 0.10-1.0 M are consistent with a previously proposed mechanism involving protonation of the carbonate ligand prior to ring-opening, but the equilibrium constant for protonation is smaller in this case than those obtai...Continue Reading

Citations

Jan 27, 2016·Inorganic Chemistry·Tomoya IshizukaTakahiko Kojima
Aug 1, 2009·Journal of the American Chemical Society·Tianzhi ZhangEric V Anslyn
May 8, 2008·Dalton Transactions : an International Journal of Inorganic Chemistry·Germán CavigliassoAllan G Blackman
Feb 10, 2010·Chemistry, an Asian Journal·Lisa F McClintock, Allan G Blackman
Dec 7, 2013·Dalton Transactions : an International Journal of Inorganic Chemistry·Yanyan MulyanaColette Boskovic
Sep 20, 2008·Dalton Transactions : an International Journal of Inorganic Chemistry·Lisa F McClintockAllan G Blackman

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