Polarizability and nuclear shielding for the sodium anion in condensed phases

The Sodium Anion Is Strongly Perturbed in the Condensed Phase Even Though It Appears Like a Free Ion in Nuclear Magnetic Resonance Experiments

“…4,9,12,18 Investigations concluded that Na − is a "genuine" anion in which both the [Ne] core and the 3s valence electrons interact very weakly with their surroundings. 16,17,19 Strong evidence for this characterization was provided by the almost complete absence of quadrupolar broadening of the 23 Na NMR signals. A quadrupolar broadening would arise from an electric field gradient (EFG) generated in Na − by a distortion of its electron density and by the presence of fluctuating nonspherical partial charge distributions from other ions and solvent molecules in the surrounding.…”

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Solvated sodium anions (Na − ) were thought to behave essentially like isolated gas-phase ions that interact only weakly with their environments. For example, 23 Na NMR signals for solvated Na − are very sharp, despite the potential for strong quadrupolar broadening. The sharp NMR signals appear to indicate a nearly spherical electron density of the ion.

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“…11−15 The resolution of the NMR experiment allows for the simultaneous identification of both the anion and the complexed cation. For instance, 23 Na NMR chemical shifts have been measured for [Na + c222Na − ] on several occasions. 4,12,16,17 The chemical shift of Na + in this system is typical of the shift detected for other sodium salts.…”

“…We estimate its gas-phase isotropic static polarizability to be over 800 times that of Na + (808 vs 1 atomic units (au), PBE/ATZP, computational details provided below), similar to previous reports. 23 In order to highlight the comparison between Na + and Na − , we calculated the radial electron probability densities D(r) = r 2 ρ(r) for Na − and Na + , shown in Figure 1 Na − radius. For example, Matalon et al 24 estimated a radius of ∼2.25 Å, and Tehan et al 5 reported a value of 2.10 Å.…”

Polarizabilities of the alkali anions: Li− to Fr−

“…3 Moreover, the structures of several salts containing alkali anions were determined by x-ray crystallography. 14 However, there is only one such calculation 19 for ␣͑Na − ͒ and only a crude uncoupled Hartree-Fock ͑UCHF͒ calculation 20 for ␣͑K − ͒. 3 No experimental values are available for the polarizabilities of the alkali anions but they have been calculated by many methods involving model or pseudopotentials.…”