Molecular view of the anomalous acidities of Sn2+, Pb2+ and Hg2+

Cox, Hazel and Stace, Anthony J (2004) Molecular view of the anomalous acidities of Sn2+, Pb2+ and Hg2+. Journal of the American Chemical Society, 126 (12). pp. 3939-3947. ISSN 0002-7863

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Experimental results taken from both the condensed and gaseous phase show that, when associated with water, the three dications Sn2+, Pb2+, and Hg2+ exhibit a facile proton-transfer reaction. In the gas phase, no stable [M.(H2O)(n)](2+) ions are observed; but instead the cations appear to undergo rapid hydrolysis to give ions of the form M+OH(H2O)(n-1). A series of ab initio calculations have been undertaken on the structures and proton-transfer reaction profiles associated with the complexes [M.(H2O)2,4](2+), where M is one of Sn, Pb, Hg, and Ca. The latter has been used as a reference point both in terms of comparisons with previous calculations, and the fact that Ca2+ is a very weak acid. The calculations show that for Sn2+, Pb2+, and Hg2+, the only barriers to proton transfer are those associated with the movement of water molecules would be sufficient. In contrast, the calculations show that for Ca2+ it is the proton-transfer step that provides the most significant reaction barrier. Proton transfer in Sn2+ and Pb2+ is further assisted by distortions in the geometries of [M.(H2O)2,4](2+) complexes due to voids created by the 5S(2) (6S(2)) inert lone pair. For Hg2+, ease of proton transfer is derived partly from the high degree of covalent bonding found in both the reactants and products.

Item Type: Article
Additional Information: HC carried out all theory work, co-authored the paper in collaboration with AJS and is joint corresponding author. First theoretical investigation into the anomalous acidities of Sn2+, Pb2+, and Hg2+, due to facile proton-transfer. Provided explanation for lack of gas phase Pb2+-water complexes and their general condensed phase behaviour.
Schools and Departments: School of Life Sciences > Chemistry
Depositing User: Hazel Cox
Date Deposited: 06 Feb 2012 18:31
Last Modified: 19 Mar 2012 10:08
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