Beryllium-9 NMR spectroscopy and molecular orbital studies of hydrogen-bonding interaction of tetraaquaberyllium(II) ion with water in the second solvation sphere in propiononitrile

摘要

The equilibrium constants of the hydrogen-bonding interactions between the tetraaquaberyllium( II) ion ([Be(H2O)(4)](2)(+)) and water in the second solvation sphere were determined from the dependence of the Be-9 NMR chemical shift (delta(Be)) on the water concentration (C-W) in propiononitrile (PN). The Be-9 NMR line assigned to [Be(H2O)(4)](2+) is downfield shifted with the increasing C-W, and the change in delta(Be) as a function of C-W is explained in terms of a two-step hydrogen-bonding interaction to form [Be(H2O)(4)](H2O)(n)(2+) (n = 1, 2). Molecular orbital calculations for [Be(H2O)(4)](H2O)(n)(2+) (n = 0 - 2) revealed that the electron density on the Be(II) ion increases with an increase in n due to an enhanced polarization of the bound water molecules accompanied by the hydrogen bonding in the second solvation sphere. The observed downfield shift of delta(Be) is interpreted as a significant compensation of the diamagnetic upfield shift by the paramagnetic contribution due to the mixing of the vacant s and p orbitals of Be with the sigma-type lone-pair orbitals of the coordinating water molecules.