Optimally solvated Na+ ions form in ethereal solutions when unsaturated hydrocarbons with extended π-systems such as perylene undergo one-electron reduction by sodium and crystallize as solvent-separated radical anion salts. The coordination number of Na+ is 6, 7, or 8 (see 1) depending on the ether used as solvent. From the structural data approximate solvation enthalpies can be calculated, which agree with laboratory experience.
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Bock et al. (1994) studied this question.
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