溶劑化電子

溶劑化電子（英語：solvated electron）也稱溶劑合電子，指的是溶液中存在的自由電子，也可被視為最小的陰離子。溶劑化電子可以在很多體系中產生，但由於其壽命很短，難以被直接觀察到^[1]。鹼金屬溶於液氨之後所得溶液的深色即源於溶劑化電子，隨溶劑化電子濃度升高，顏色由藍色逐漸轉變為銅色（鹼金屬濃度大於3mol/L時）^[2]。一般對溶劑化電子的討論限於金屬-液氨體系，因為它們在其中的壽命可達數天，但水和其它溶劑中也存在着溶劑化電子。

歷史

1807-1809年間漢弗萊·戴維在氨氣中加入鉀的晶粒，第一次觀察到了溶劑化電子所造成的顏色。1879-1880年間詹姆斯·巴蘭坦·漢內（英語：James Ballantyne Hannay）和J. Hogarth使用鈉重複了戴維的實驗。1907年查爾斯·A·克勞斯（英語：Charles A. Kraus）測量了金屬-液氨溶液的電導率，首先將電導率的變化歸結為金屬電離出的自由電子^[3]^[4]。1918年G. E. Gibson和W·L·阿爾戈提出了溶劑化電子的概念^[5]。他們注意到，根據吸收光譜，不同的金屬在不同的溶劑如甲胺和乙胺中可以產生相同的藍色，表明是由同一種物質，溶劑化電子導致的。1970年，科學家表徵了包含電子化合物的固體鹽。^[6]

性質

鹼金屬以及鈣、鍶、鋇、釔等的液氨溶液，均因為溶劑化電子的存在顯藍色^[7]。

鋰在零下60度的液氨中的溶解度是16 mol% metal (MPM)。當鋰的濃度升高時，溶液的電導率從 10⁻²升高到了10⁴ 歐姆⁻¹厘米⁻¹ (比水銀的電導率還要高)。在8 MPM附近時，會發生金屬態轉變。在 4 MPM 時，發生液相分離，淺金色的緻密相從藍色的基相中分離出來。當濃度大於8 MPM，溶液是青銅/金色的，密度下降了大概30%.

溶劑化電子的標準電極電勢是-2.77 V.^[8] 等效電導率是177 Mho cm²，與氫氧根離子相當。溶劑化電子在液氨中的擴散係數可以通過計時安培分析法（英語：chronoamperometry）測得。^[9]這一電導率對應的擴散率為4.75×10⁻⁵ cm²s⁻¹^[10]。

反應與應用

溶劑化電子可以與氧原子反應，形成超氧自由基（O₂^.−）。^[11]遇到一氧化氮，溶劑化電子可以形成羥基自由基（HO^.）。^[12]鈉溶於液氨之後形成的具有溶劑化電子的溶液的通常應用是伯奇還原，而鈉在乙醇中進行的布沃－布朗還原反應也被認為有溶劑化電子的作用。

參考文獻

^ Schindewolf, U. Formation and Properties of Solvated Electrons. Angewandte Chemie International Edition in English. 1968, 7 (3): 190. doi:10.1002/anie.196801901.
^ Cotton, F.A; G. Wilkinson. Advanced Inorganic Chemistry. John Wiley and Sons Inc. 1972. ISBN 0-471-17560-9.
^ Kraus, Charles A. Solutions of Metals in Non-Metallic Solvents; I. General Properties of Solutions of Metals in Liquid Ammonia. J. Am. Chem. Soc. 1907, 29 (11): 1557–1571. doi:10.1021/ja01965a003.
^ Zurek, Eva. A Molecular Perspective on Lithium–Ammonia Solutions. Angew. Chem. Int. Ed. 2009, 48 (44): 8198–8232. doi:10.1002/anie.200900373.
^ Gibson, G. E.; Argo, W. L. The Absorption Spectra of the Blue Solutions of Certain Alkali and Alkaline Earth Metals in Liquid Ammonia and Methylamine. J. Am. Chem. Soc. 1918, 40 (9): 1327–1361. doi:10.1021/ja02242a003.
^ Dye, J. L. Electrons as Anions. Science. 2003, 301 (5633): 607–608. PMID 12893933. doi:10.1126/science.1088103.
^ Combellas, C; Kanoufi, F; Thiébault, A. Solutions of solvated electrons in liquid ammonia. Journal of Electroanalytical Chemistry. 2001, 499: 144. doi:10.1016/S0022-0728(00)00504-0.
^ Baxendale, J. H. (1964) , Radiation Res. Suppl., 114 and 139. [2018-09-07]. （原始內容存檔於2021-12-19）.
^ 存档副本. [2018-09-05]. （原始內容存檔於2019-06-05）.
^ Survey of Progress in Chemistry p 148
^ Hayyan, M.; Hashim M. A.; AlNashef I. M. Superoxide Ion: Generation and Chemical Implications. Chem. Rev. 2016, 116: 3029–3085. doi:10.1021/acs.chemrev.5b00407.
^ Janata, E.; Schuler, Robert H. Rate constant for scavenging eaq- in nitrous oxide-saturated solutions. J. Phys. Chem. 1982, 86 (11): 2078–84. doi:10.1021/j100208a035.

Sagar, D. M.; Colin; Bain, D.; Verlet, Jan R. R. Hydrated Electrons at the Water/Air Interface. J. Am. Chem. Soc. 2010, 132 (20): 6917–6919. doi:10.1021/ja101176r.
Martyna, Glenn. Electronic states in metal-ammonia solutions. Physical Review Letters. 1993, 71 (2): 267. Bibcode:1993PhRvL..71..267D. doi:10.1103/physrevlett.71.267.
Martyna, Glenn. Quantum simulation studies of singlet and triplet bipolarons in liquid ammonia. Journal of Chemical Physics. 1993, 98 (1): 555–563. Bibcode:1993JChPh..98..555M. doi:10.1063/1.464650.
Martyna, Glenn. Quantum simulation studies of metal–ammonia solutions. Journal of Chemical Physics. 1994, 100 (10): 7590–7601. Bibcode:1994JChPh.100.7590D. doi:10.1063/1.466852.
Solvated Electron. Advances in Chemistry 50. 1965. ISBN 978-0-8412-0051-7. doi:10.1021/ba-1965-0050.
Anbar, Michael. Reactions of the Hydrated Electron. Solvated Electron. Advances in Chemistry 50. 1965: 55. ISBN 0-8412-0051-3. doi:10.1021/ba-1965-0050.ch006.
Abel, B.; Buck, U.; Sobolewski, A. L.; Domcke, W. On the nature and signatures of the solvated electron in water. Phys. Chem. Chem. Phys. 2012, 14 (1): 22–34. Bibcode:2012PCCP...14...22A. PMID 22075842. doi:10.1039/C1CP21803D.
Determination of the Chemical Solvation Energy of the Solvated Electron. Journal of Electroanalytical Chemistry 129. 1981. doi:10.1016/S0022-0728(81)80027-7.
Survey of Progress in Chemistry, chapter 5, 129, 1969 [first page https://www.sciencedirect.com/sdfe/pdf/download/eid/1-s2.0-B9780123957061500108/first-page-pdf] and content preview [1] （頁面存檔備份，存於互聯網檔案館）
The electrochemistry of the solvated electron Technische Universiteit Eindhoven https://pure.tue.nl/ws/files/2089318/388448.pdf （頁面存檔備份，存於互聯網檔案館）
IAEA On the Elextrolytic Generation of Hydrated Electron [2] （頁面存檔備份，存於互聯網檔案館）
Fundamentals of Radiation Chemistry, chapter 6, p 145-198, Academic Press, 1999 [3] （頁面存檔備份，存於互聯網檔案館）

[1] Schindewolf, U. Formation and Properties of Solvated Electrons. Angewandte Chemie International Edition in English. 1968, 7 (3): 190. doi:10.1002/anie.196801901.

[c&w-2] Cotton, F.A; G. Wilkinson. Advanced Inorganic Chemistry. John Wiley and Sons Inc. 1972. ISBN 0-471-17560-9.

[3] Kraus, Charles A. Solutions of Metals in Non-Metallic Solvents; I. General Properties of Solutions of Metals in Liquid Ammonia. J. Am. Chem. Soc. 1907, 29 (11): 1557–1571. doi:10.1021/ja01965a003.

[4] Zurek, Eva. A Molecular Perspective on Lithium–Ammonia Solutions. Angew. Chem. Int. Ed. 2009, 48 (44): 8198–8232. doi:10.1002/anie.200900373.

[5] Gibson, G. E.; Argo, W. L. The Absorption Spectra of the Blue Solutions of Certain Alkali and Alkaline Earth Metals in Liquid Ammonia and Methylamine. J. Am. Chem. Soc. 1918, 40 (9): 1327–1361. doi:10.1021/ja02242a003.

[6] Dye, J. L. Electrons as Anions. Science. 2003, 301 (5633): 607–608. PMID 12893933. doi:10.1126/science.1088103.

[7] Combellas, C; Kanoufi, F; Thiébault, A. Solutions of solvated electrons in liquid ammonia. Journal of Electroanalytical Chemistry. 2001, 499: 144. doi:10.1016/S0022-0728(00)00504-0.

[8] Baxendale, J. H. (1964) , Radiation Res. Suppl., 114 and 139. [2018-09-07]. （原始內容存檔於2021-12-19）.

[9] 存档副本. [2018-09-05]. （原始內容存檔於2019-06-05）.

[10] Survey of Progress in Chemistry p 148

[11] Hayyan, M.; Hashim M. A.; AlNashef I. M. Superoxide Ion: Generation and Chemical Implications. Chem. Rev. 2016, 116: 3029–3085. doi:10.1021/acs.chemrev.5b00407.

[12] Janata, E.; Schuler, Robert H. Rate constant for scavenging eaq- in nitrous oxide-saturated solutions. J. Phys. Chem. 1982, 86 (11): 2078–84. doi:10.1021/j100208a035.

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