| Popis: |
The conventional chemical definition of an alkali metal in solution is based on the tacit assumption of cation formation through the spontaneous ionization of the ns1 valence electron1. However, much experimental evidence, both direct and indirect, has accumulated over the past decade for the existence of the anionic form of the alkali elements in certain non-aqueous solutions2. In 1974, Ceraso and Dye3 reported the fingerprint nuclear magnetic resonance (NMR) spectrum of the sodium anion, Na−, which constituted the first direct proof of the existence of this ion in solution. Since then, high-resolution multi-element NMR spectroscopy has been used to identify the ubiquitous Na− ions4–7, as well as the rubidide (Rb−) (refs 4, 7) and caeside (Cs−) ions4 in a variety of metal solution systems both liquid and solid8,9. Until now, the status of the potasside ion, K−, has been unclear. We report here the first observation of the 39K-NMR spectrum of K− from solutions of potassium metal and potassium/caesium mixed metals in the liquid crown ethers, 1,4,7,10-tetraoxacyclododecane (12-crown-4, 12C4) and 1,4,7,10,13-pentaoxacyclopentadecane (15-crown-5, 15C5). This constitutes the first direct proof of the existence of K−; the NMR data also give detailed information on the microscopic electronic structure of the potassium anion in solution. |
