行政院國家科學委員會補助專題研究計畫成果報告
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二茂鐵化學(IV)
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計畫類別：■個別型計畫
□整合型計畫
計畫編號：NSC90－2113－M－110－014－
執行期間：
90 年 08 月 01 日至 91 年 07 月 31 日
計畫主持人：董騰元
共同主持人：
計畫參與人員：
本成果報告包括以下應繳交之附件：
□赴國外出差或研習心得報告一份
□赴大陸地區出差或研習心得報告一份
□出席國際學術會議心得報告及發表之論文各一份
□國際合作研究計畫國外研究報告書一份
執行單位：國立中山大學化學系
中
華
民
國
91
年 10 月 15 日
Progress Repor t
This section will begin a listing of papers published in the past year. Following the listing, only the most important results of the works supported by the National Science Council will be mentioned.
(I) Paper Published (2001-2002)
(67) Dong, T.-Y.; Lee, L.; Cheng, C. H.; Chang, L. S.; Chiang, M. Y. "Complexation Behavior of 1,1'':1',1'''-Bis(1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diyldimethyl)-bisferrocene: Structural Determination, NMR, 57Fe Mössbauer and Electrochemical Measurements",J . Organomet. Chem. 2001, 625, 173.
(68) Dong, T.-Y.; Lee, T. J.; Huang, B. R.; Peng, S. M.; Lee, G. H. "Pronounced Effects
of Counterions on Intramolecular Electron Transfer in 1',1'''-Dinaphthyl-methylbiferrocenium Cation", Inorg. Chem. Comm. 2001, 4, 82.
(69) Dong, T.-Y.; Chang, L. S.; Lee, G. H.; Peng, S. H. "57Fe Mössbauer Spectroscopic and X-ray Structural Analyses on the Mixed-Valence State of Biferrocenium Derivatives with Bromoalkyl Substituents", Inorg. Chem. Comm. 2002, 5, 107.
(70) Dong, T.-Y.; Chang, L. S.; Lee, G. H.; Peng, S. M. "Pronounced Effects of
Zero-Point Energy Difference on Intramolecular Electron Transfer in Asymmetric Mixed-Valence Biferrocenium Cations : Structural, EPR, and 57Fe Mössbauer Characteristics", Organometallics 2002, accepted.
(71) Dong, T.-Y.; Huang, B. R.; Peng, S. M.; Lee, G. H.; Chiang, M. Y. "Effects of
counterions on intramolecular electron transfer in
1',1'''-dinaphthylmethyl-biferrocenium cation: structural, Mössbauer and EPR characteristics",J . Organomet. Chem. 2002, accepted.
(II) Results of Published Wor ks (2000-2001)
(a) Prepar ation of nanopar ticle :
想作出均勻的 Au nanoparticles 似乎不是想像中的那麼簡單，且其再現性也 是一大挑戰，這也是每一個研究奈米科技 group 最頭痛的問題，我們也作出一些 較均勻的 Au nanoparticle 其 TEM 如下圖，而且某些 condition 下似乎也可以長出 棒狀之 Au 棒(化學方法)。
(b) 最近結果
The self-organization of various functionalized alkanethiols chemisorbed on two-dimensional Au surfaces has been extensively investigated. The chemisorbed of ferrocene-terminated alkanethiols with nonelectroactive n-alkanethiols on evaporated gold
films improves the overall ordering of the adsorbed layer by constraining the ferrocene groups to a fixed position. An important recent report describing the stabilization of Au cluster with chemisorbed alkanethiols opens the way to study of three-dimensional monolayers by conventional methodologies such as NMR spectroscopy. In particular, alkanethiolate Au clusters are stable in air, soluble in nonpolar organic solvents, and
capable of facile modification with other thiols through exchange reactions. Following the initial report by Nishihara on a synthesis of biferrocene derivative-modified Au cluster 1, this paper describes the spectroscopic and electrochemical characterizations of a stable biferrocene-modified Au cluster 2, and chemisorbed biferrocenylalkanethiols on Au(111) surface 3.
The biferrocene-modified Au cluster 1 undergoes two-step one-electron oxidation processes in CH2Cl2 solution. Furthermore, the shape of the voltammogram changes
gradually during the potential scans, and it converges finally into one broaden redox wave. We suspect the stability of the Au cluster 1 in CH2Cl2 solution during the potential scans.
Our results indicate that the chemically oxidized dication of acylbiferrocenium is not quite electrochemically stable in organic solvents. Our strategy is the use of redox stable biferrocenylalkanethiol attached to the Au cluster and Au(111) surface.
S R S R S S S R S S R S R S R S S S R S R S R S R S R S R S S S S S S R C S (CH2)7 O S Fe Fe (1) : -C8H17S S R : S (CH2)6 S Fe Fe (2) : -C6H13S S R : S (CH2)6 S Fe Fe (3) : -C6H13S S R :
Gold cluster 2 was prepared by substitution method of hexanethiol-stabilized Au cluster developed by Murray. A TEM image of 2 indicates that the core size of the cluster is ~2.2 nm corresponding to 309 Au atoms. It is proposed that the number of hexanethiolate units on one cluster is in the range 63~65 estimated from the elemental analysis data, the number of biferrocenylhexanetholate units on the cluster is 9 estimated from the ICPMS. The IR spectra of the Au cluster 2 and of biferrocenylhaexanethiol are similar, which indicates that the biferrocenylthiol is indeed part of the composite.
When the cyclic potential scans are carried out in DME solution of 2, two successive reversible one-electron redox waves were observed (E1/2 = 0.47; 0.78 V vs Ag+/Ag). The
two redox waves increase slightly in size with repeated scanning (100 mvs-1), donating electrodeposition of a redox-active film. When the voltammetry is carried out at different scan rates, the positive and negative current peaks for each redox wave occur at almost the same potential (peak-to-peak separation ~30 mv) and the peak current increases almost linearly with the sweep rate, implying that the Au cluster is adsorbed on the electrode surface. The magnitude of the peak separation between two waves (△E1/2) gives an
indication of the interaction between the two Fe sites. In the case of free biferrocenylhexanethiol, the two reversible redox waves (E1/2) were observed at 0.45 and
0.78 V. A comparison of the magnitude of △E1/2 of biferrocenylhexanethiol (0.33 V ) and
the Au cluster 2 (0.31 V ) reveals that the magnitude of the interaction between the two Fe sites in the Au cluster is smaller. We suggest that this difference in Fe-Fe interaction between solution state and structurally defined self-assembled Au cluster is a result of difference in the degree of reorganization energy.
Electrochemical measurements were also made for the chemisorbed biferrocenyl-hexanethiol on Au(111) surface (3) in a cell in which a 0.61cm2 glass tube was pressed down against the Au(111) surface. The electrolyte (1 M HClO4), the counter electrode (Pt),
were observed (E1/2 = 0.25 and 0.51V). Repeated rescanning (100 mVs-1) does not change
the voltammograms, demonstrating that the monolayer is stable to electrochemical cycling in 1M HClO4 solution. The peak-to-peak separation for each wave is ~20 mV and the peak
current increases linearly with the sweep rate. From the similarities of the electrochemical measurements between 3D-SAM Au cluster and biferrocenylhexanethiol monolayer on 2D-SAM Au(111) surface, it arises the question whether the character on alkane chain ordering on the planer Au(111) surface shows intrinsic differences from the Au cluster (owing to the surface curvature) or not. A comparison of the △ E1/2 value of the
biferronylhexanethiol on Au(111) ( 0.26V ) and the Au cluster 2 ( 0.31V ) indicates that the interaction between the two Fe centers in the monolayer on Au(111) surface is smaller. We suggest that this is a result of difference in the degree of reorganization energy between “solid-like” biferrocenylhexanethiol on Au(111) surface and the “solution-like” Au cluster. The coverage of biferrocenyl sites on the Au(111) surface evaluated from the peak area of cyclic voltammogram is 3.5×10-10 molcm-2. A study of coadsorption of ferrocene-terminated alkanethiols with unsubstituted alkanethiols on evaporated Au films was supported by Chidsey. Lower concentrations of alkanethiols linked to ferrocene (Fc) by a polar ester group (FcCO2(CH2)nSH) show ideal surface electrochemistry in 1 M HClO4
and higher concentrations or use of alkanethiols linked directly to the nonpolar ferrocene group (Fc(CH2)nSH) lead to broadened and asymmetry electrochemical features. In Figure
2b, as the mole fraction of biferrocenylhexanethiol (÷bifc) is equal to 1, the first and second
redox waves are nearly symmetric with a full width at half maximum of ~120 and 150mV, respectively, and with ~20 mV peak-to-peak separation. Using biferrocenylhexanethiol and hexanethiol as coadsorbates results on very similar cyclic voltammograms for ÷bifc = 0.25,
0.1, and 0.067. Ideal redox peaks are symmetric with ~90 mV full width at half maximum and with no splitting between the oxidation and reduction peaks.
