Aqueous divalent metal-nitrate interactions: hydration versus ion pairing.
Nitrate aqueous solutions, Mg(NO(3))(2), Ca(NO(3))(2), Sr(NO(3))(2), and Pb(NO(3))(2), are investigated using Raman spectroscopy and free energy profiles from molecular dynamics (MD) simulations. Analysis of the in-plane deformation, symmetric stretch, and asymmetric stretch vibrational modes of the nitrate ions reveal perturbation caused by the metal cations and hydrating water molecules. Results show that Pb(2+) has a strong tendency to form contact ion pairs with nitrate relative to Sr(2+), Ca(2+), and Mg(2+), and contact ion pair formation decreases with decreasing cation size and increasing cation charge density: Pb(2+) > Sr(2+) > Ca(2+) > Mg(2+). In the case of Mg(2+), the Mg(2+)-OH(2) intermolecular modes indicate strong hydration by water molecules and no contact ion pairing with nitrate. Free energy profiles provide evidence for the experimentally observed trend and clarification between solvent-separated, solvent-shared, and contact ion pairs, particularly for Mg(2+) relative to other cations.
Published In/Presented At
Xu, M., Larentzos, J. P., Roshdy, M., Criscenti, L. J., & Allen, H. C. (2008). Aqueous divalent metal-nitrate interactions: hydration versus ion pairing. Physical chemistry chemical physics : PCCP, 10(32), 4793–4801. https://doi.org/10.1039/b807090n
Medicine and Health Sciences
Department of Surgery