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Synthesis and determination of the electron transfer numbers of alkynyl bridged multiferrocenyl derivatives
Inorganic Chemistry Communications 11 (2008) 873–875
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Synthesis and determination of the electron transfer numbers of alkynyl bridged multiferrocenyl derivatives Li-Min Han *, Quan-Ling Suo, Mei-hua Luo, Ning Zhu, Yan-Qiang Ma Chemical Engineering College, Inner Mongolia University of Technology, Hohhot, 010051, PR China
a r t i c l e
i n f o
Article history: Received 25 March 2008 Accepted 14 April 2008 Available online 27 May 2008 Keywords: Ferrocenylacetylene derivatives Electron transfer Chronoamperometry Cyclic voltammogram Cottrell plot
a b s t r a c t Multiferrocenyl derivatives FcC(CH3)2Fc0 –C„C–Fc(A) (Fc = C5H5FeC5H4, Fc0 = C5H5FeC5H3) and FcC(CH3)2Fc0 –C„C–C„C–Fc0 C(CH3)2Fc (B) have been synthesized and characterized by MS, NMR, FT-IR and elemental analysis. The molecular structure of compound A was given by single crystal X-ray diffraction. The electron transfer numbers of two compounds were determined by cyclic voltammetry and chronoamperomeric technique. Ó 2008 Elsevier B.V. All rights reserved.
Multi-redox-center molecules, especially those multiferrocenyl derivatives with electron interaction, have attracted considerable interest because of their potential applications in electron reservoirs and molecular electronic devices [1–3]. The electron interaction or the charge delocalization of multiferrocenyl derivatives have been explored in terms of investigating electron transfer numbers of each ferrocenyl unit in the molecules [4–6]. However, when ferrocenyl units were assembled into one molecule, the electron transfer processes of multiferrocenyl derivatives became unintelligible due to the charge transfer became more complicated [7–9]. Thus, looking after an effective and advantaged method to determine the electron transfer numbers of multiferrocene in an electrode reaction are indispensable. Traditionally, electron transfer numbers were electrochemically determined by Nernst plot or by the evaluation of the amount of redox charge in bulk electrolysis. Though bulk electrolysis seems to be a reliable method, time-consuming, side reactions and solution resistance lower its accuracy. Fortunately, with the evolution of microelectrode techniques, Kakihana devised a chronoamperomeric method for evaluating electron transfer numbers by using of the microelectrode [10]. The chronoamperomeric method is based on taking the ratio of slope (s) to intercept (p) in the Cottrell plots. When the chronoamperometry was performed at various potentials of normal pulse voltammetry, the electron transfer numbers could be obtained at each potential [11–15]. In this paper, multiferrocenyl derivatives FcC(CH3)2Fc0 –C„C–Fc (A) (see Scheme 1) were synthesized and characterized by FT-IR, * Corresponding author. Tel.: +86 471 6575675; fax: +86 471 6575796. E-mail addresses: [email protected], [email protected] (L.-M. Han). 1387-7003/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2008.04.017
NMR, MS and element analysis [16,17], and the molecular structure of A was confirmed by single-crystal X-ray analysis [18], and FcC(CH3)2Fc0 –C„C–C„C–Fc0 C(CH3)2Fc (B) was synthesized according to the documental methods [19]. All manipulations were performed under a dry argon atmosphere using conventional Schlenk techniques, reagents of FcC(CH3)2Fc0 –C„CH, FcI, FcC(CH3)2Fc0 –C„CCu were synthesized according to the literatures and solvents were purified, dried and distilled under argon atmosphere prior to be used [20,21] (Fig. 1). According to the documental methods, the Cottrell plot (I vs. t1/2) at a microelectrode gives out s and p, where s ¼ p1=2 nD1=2 Fa2 c ð1 þ e1 Þ1 ; p ¼ pnFDac ð1 þ e1 Þ1 ; 1 ¼ ðF=RTÞðE E0 Þ. The electron transfer number can be obtained from n ¼ s2 =pFa3 c ð1 þ e1 Þ1 [22–24]. In order to confirm the validity of this method, the cyclic voltammetric and chronoamperometric properties of ferrocene were investigated with a microelectrode (d = 0.025 mm). The cyclic voltammograms showed that redox peaks of ferrocene theoretically disappeared with decreasing of scan rate (see Fig. 2) [24]. In the time domain from 0.1 to 10 s, the chronoamperometry was carried out by the potential stepping from 0.2 to 0.4, 0.2, 0.1, 0.0 V, respectively. The Cottrell plots were close to a linear relation in the time domain from 0.3 to 3.0 s while the background current was subtracted (see Fig. 3). On the assumption of 1 ! 1, we can calculate the s and p values by the formulas, then the electron transfer numbers were finally obtained by, n ¼ s2 =pFa3 c ð1 þ e1 Þ1 , which near to the theoretic value 1 (see Fig. 2) [23]. Therefore, this method was available for the determination of electron transfer number of ferrocenyl derivatives.
874
L.-M. Han et al. / Inorganic Chemistry Communications 11 (2008) 873–875
-e
a
b
-e
-e
FcC(CH3)2Fc'C2Fc
FcC(CH3)2Fc'C2Fc
FcC(CH3)2Fc'C2Fc
c
FcC(CH3)2Fc'C2Fc
A -2e
FcC(CH3)2Fc'C4Fc'(CH3)2CFc
a'
b'
c'
FcC(CH3)2Fc'C4Fc'(CH3)2CFc
d'
-e -e FcC(CH3)2Fc'C4Fc'(CH3)2CFc
FcC(CH3)2Fc'C4Fc'(CH3)2CFc
B Scheme 1. Redox processes of compounds A and B.
Fig. 1. Molecular structure of compound A and it is selected bond lengths [Å] and angles [°], C(10)–C(11) 1.508, C(11)–C(14) 1.537, C(16)–C(17) 1.428, C(17)–(C24) 1.448, (C24)–C(25) 1.208, C(25)–C(26) 1.428; C(10)–C(11)–C(12) 110.6, C(16)–C(17)–C(24) 126.6, C(24)–C(25)–C(26) 177.2, C(10)–C(11)–C(14) 106.5, C(17)–C(24)–C(25) 179.7, C(25)–C(26)–C(27) 126.7.
[×10 -7 ]
0.1
I/A
1
0
0
a
I / μA
n ( 1+e-ξ)-1
1
b c d
0 0
-0.2
0
0.2
0.4
E / V vs SCE Fig. 2. Cyclic voltammogram of 2.0 mM ferrocene + 0.2 M TBAP in acetonitrile and THF(v:v 10:1) at scan rate of 1 V s1 and 0.01 V s1 in the left ordinate. Values of nð1 þ e1 Þ1 (O in the right ordinate) obtained from the Cottrell plot.
The electron transfer numbers of compounds A and B were evaluated by the above method. The cyclic voltammograms of compounds A and B were shown in Fig. 4, both of them exhibited three well-defined waves, and the redox processes were deduced in Scheme 1. For compound A, since the bridged isopropyl carbon atom linked ferrocenyl unit a and b is an electron donor, the first oxidation should be ascribed to the ferrocenyl unit a, the second oxidation should be ascribed to the ferrocenyl unit b and the third oxidation come from ferrocenyl unit c. The higher oxidation potential of ferrocenyl unit c may be originated from the combination of the withdrawing electron function of alkynyl group and ferrocenium formed in second oxidative step, and all oxidations are one step one electron process. The potential difference between ferrocenyl unit b and c is about 130 mV, which consist
1 -1/2
t
2 -1/2
/s
Fig. 3. Cottrell plots of the background-sunstracted currents for 2.0 mM ferrocene + 0.2 M TBAP in acetonitrile and THF(v:v 10:1) when potential was stepped from (a) 0.2 to 0.4 V, (b) 0.2 to 0.2 V, (c) 0.2 to 0.1 V, (d) 0.2 to 0.0 V.
with the literature [25]. For compound B, ferrocenyl unit a0 and d0 are symmetric and non-conjugated, therefore, the first oxidation step maybe occurrs on this two ferrocenyl units, and it is one step two electron process. The second oxidation may come from the conjugated ferrocenyl unit b0 or c0 , if it comes from ferrocenyl unit b0 , the third oxidation should occur on ferrocenyl unit c0 , and each of them is one step one electron process. The potential difference of ferrocenyl unit b0 and c0 is about 100 mV, which is also consistent with the literature [25]. In order to identify the assumption of electron transfer processes in cyclic voltammetry, the chronoamperometry of compounds A and B were performed by stepping potentials from 0.2 to 0.1, 0.1 to 0.3 and 0.3 to 0.6 V, similar to that of ferrocene at a microelectrode (see Fig. 2). The Cottrell plots of the background-subtracted current of compound A were shown in Fig. 5,
L.-M. Han et al. / Inorganic Chemistry Communications 11 (2008) 873–875
875
method to determine the electron transfer numbers of multiferrocenyl derivatives.
B
I / μA
4 A
Acknowledgements
2 We are grateful to the Specialized Research Fund for the Doctoral Program of Higher Education of China (20060128001), the Natural Science Fund of Inner Mongolia (200711020201) and Specialized Research Fund of Inner Mongolia University of Technology (ZD200704).
0 -2 0
0.2 0.4 E / V vs SCE
0.6 Appendix A. Supplementary material
Fig. 4. Cyclic voltammograms of 2.0 mM (A) and (B) +0.2 M TBAP in mixture of acetonitrile and THF (v:v 10:1) at scan rate of 100 mV s1.
CCDC 638454 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2008. 04.017.
0.1
I /μA
References
0
1
2
t
-1/2
/s
3
-1/2
Fig. 5. Cottrell plots of the background-sunstracted currents for 2.0 mM compound (A) +0.2 M TBAP in acetonitrile and THF (v:v 10:1) when potential was stepped from (a) 0.2 to 0.1 V, (b) 0.1 to 0.3 V, (c) 0.3 to 0.6 V.
2
I / μA
0.05
1 0 0 -0.2
0
0.2 0.4 0.6 E / V vs SCE
0.8
Fig. 6. Electron transfer number, n (O), obtained from the Cottrell plots (Fig. 5) in the right ordinate and the nearly steady state voltammogram of compound A at scan rate 0.01 V s1 in the left ordinate.
and all plots are close to linear in the time domain from 0.3 to 3 s. As the linearity was valid for determination of s and p, the electron transfer numbers can be obtained by s and p. For compound A, the average electron transfer number (represented by symbol ‘‘O”, see Fig. 6) of each steps is near to 1. Moreover, the same experiment was performed on compound B, results showed that the electron transfer numbers of the first steps is 2, and the number of the second and the third steps is 1. The results confirmed that our assumptions on electron transfer number of A and B in cyclic voltammetry are reasonable, and the chronoamperometric technique of microelectrode is an effective
[1] J.B. Flanagan, S. Margel, A.J. Bard, F.C. Anson, J. Am. Chem. Soc. 100 (1978) 4248. [2] A. Tarrasa, P. Molina, D. Curiel, M.D. Velasco, Organometallics 20 (2001) 2145. [3] P.A. Chase, R.G. Gebbink, G. Van Koten, J. Organomet. Chem. 689 (2004) 4016. [4] G. Brown, M. Meyer, T.J. Cowan, D.O. Le, C. Vanda, P.V. Roling, M.D. Rausch, Inorg. Chem. 14 (1975) 506. [5] D.O. Cowan, C.V. Le, J. Park, F. Kaufman, J. Acc. Chem. Res. 6 (1973) 1. [6] U.T. Muller-Westerhoff, Angew. Chem. Int. Ed. Engl. 25 (1986) 702. [7] C. Díaz, I. Izquierdo, M.L. Valenzuela, N. Yutronic, Inorg. Chem. Commun. 3 (2000) 525. [8] J. Borgdorff, E.J. Ditzel, N.W. Duffy, B.H. Robinson, J. Simpson, J. Organomet. Chem. 437 (1992) 323. [9] M.H. Delville, F. Robert, P. Gouzerh, J. Linares, et al., J. Organomet. Chem. 451 (1993) 10. [10] M. Kakihana, H. Ikeuchi, G.P. Sato, et al., J. Electroanal. Chem. 117 (1981) 201. [11] W.T. Yap, L.M. Doane, Anal. Chem. 54 (1982) 1437. [12] G. Denuault, M.V. Mirkin, A.J. Bard, J. Electroanal. Chem. 308 (1991) 27. [13] S. Dong, H. Zhou, J. Electroanal. Chem. 403 (1996) 117. [14] J.V. Macpherson, P.R. Unwin, Anal. Chem. 69 (1997) 2063. [15] W. Hyk, A. Nowicka, Z. Stojek, Anal. Chem. 74 (2002) 149. [16] Synthesis of FcC(CH3)2Fc0 –C„C–Fc (A): FcC(CH3)2Fc0 –C„CCu (100 mg, 0.2 mmol) and FcI (94 mg, 0.3 mmol) were dissolved in 15 ml pyridine. The mixture solution was stirred and refluxed for 8 h, then be poured into water (50 ml) at 0. The resulting mixture was extracted by CH2Cl2. The organic phase were incorporated, then washed by 2 M HCl and H2O, respectively, and dried by using dehydrated MgSO4, and filtrated. The filtrate was concentrated and the residue was subjected to chromatographic separation on the neutral alumina column (2.0 30 cm). Elution with a mixture of hexane–ether (2:1, v/ v) afforded a yellow band. The yellow crystal of FcC(CH3)2Fc0 –C„C–Fc was obtained by re-crystallizing from hexane-CH2Cl2. Yield, 86%; m.p., 245–246. Anal. Calc. for C35H32Fe3: C, 67.78; H, 5.20%. Found: C, 67.97; H, 5.34%. IR (KBr disk, cm1): m(C„C) 2217.9 (w), m(CH3) 2858.0 (w), 2919.5 (m), 2965.6 (s). 1 HNMR (DCCl3, d): 4.03–4.45 (26H, m, Fc or Fc0 ), 1.61–1.68 [6H,m,C(CH3)2]. 13 CNMR (DCCl3, d): 83.66, 84.26 (C„C), 64.79, 66.11, 67.89, 68.45, 69.37, 70.56, 71.67 (Fc or Fc0 ), 30.32, 33.24[C(CH3)2]. MS (EI, m/z, Relative Abundance): 620 (M+, 44%). [17] 1H and 13C NMR spectra in CDCl3 were obtained on an Inova 500 M spectrometer operating in the FT mode. The mass spectra were determined by using of a Polaris Q-MS and a Micromass ultima-TOF instrument. IR spectra were recorded on a Nicolet FT-IR spectrometer as KBr discs. The cyclic voltammogram (CV) were obtained with a CHI-760C analyzer. [18] Crystal data: C35H32 Fe3, M = 620.16, orthorhombic, Space group P2(1), a = 7.461(10), b = 10.819(14), c = 33.54(4) Å, V = 2708(6) Å3, T = 293(2)K, Z = 4, Final R indices [I > 2(I)] R1 = 0.0548, wR2 = 0.1310, Goodness-of-fit on F2 = 1.092, Range for data collection (h)1.98 to 25.01. [19] Y.B. Wang, N. Zhu, Q.L. Suo, L.M. Han, J. Coord. Chem. 60 (2007) 2265. [20] M. Rosenblum, N. Brawn, J. Papenmeier, M. Applebaum, J. Organomet. Chem. 6 (1966) 173. [21] K. Aoki, J. Osteryoung, J. Electroanal. Chem. 160 (1984) 335. [22] K. Aoki, J. Osteryoung, J. Electroanal. Chem. 122 (1981) 19. [23] T. Nishiumi, M.M. Abdul, Electrochem. Commun. 7 (2005) 213. [24] K. Aoki, K. Akimoto, K. Tokuda, J. Osteryoung, J. Electroanal. Chem. 171 (1984) 219. [25] L.V. Carole, O. Dwaine, C. Cowan, B. Klaus, J. Am. Chem. Soc. 96 (1974) 6788.
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Synthesis and determination of the electron transfer numbers of alkynyl bridged multiferrocenyl derivatives Li-Min Han *, Quan-Ling Suo, Mei-hua Luo, Ning Zhu, Yan-Qiang Ma Chemical Engineering College, Inner Mongolia University of Technology, Hohhot, 010051, PR China
a r t i c l e
i n f o
Article history: Received 25 March 2008 Accepted 14 April 2008 Available online 27 May 2008 Keywords: Ferrocenylacetylene derivatives Electron transfer Chronoamperometry Cyclic voltammogram Cottrell plot
a b s t r a c t Multiferrocenyl derivatives FcC(CH3)2Fc0 –C„C–Fc(A) (Fc = C5H5FeC5H4, Fc0 = C5H5FeC5H3) and FcC(CH3)2Fc0 –C„C–C„C–Fc0 C(CH3)2Fc (B) have been synthesized and characterized by MS, NMR, FT-IR and elemental analysis. The molecular structure of compound A was given by single crystal X-ray diffraction. The electron transfer numbers of two compounds were determined by cyclic voltammetry and chronoamperomeric technique. Ó 2008 Elsevier B.V. All rights reserved.
Multi-redox-center molecules, especially those multiferrocenyl derivatives with electron interaction, have attracted considerable interest because of their potential applications in electron reservoirs and molecular electronic devices [1–3]. The electron interaction or the charge delocalization of multiferrocenyl derivatives have been explored in terms of investigating electron transfer numbers of each ferrocenyl unit in the molecules [4–6]. However, when ferrocenyl units were assembled into one molecule, the electron transfer processes of multiferrocenyl derivatives became unintelligible due to the charge transfer became more complicated [7–9]. Thus, looking after an effective and advantaged method to determine the electron transfer numbers of multiferrocene in an electrode reaction are indispensable. Traditionally, electron transfer numbers were electrochemically determined by Nernst plot or by the evaluation of the amount of redox charge in bulk electrolysis. Though bulk electrolysis seems to be a reliable method, time-consuming, side reactions and solution resistance lower its accuracy. Fortunately, with the evolution of microelectrode techniques, Kakihana devised a chronoamperomeric method for evaluating electron transfer numbers by using of the microelectrode [10]. The chronoamperomeric method is based on taking the ratio of slope (s) to intercept (p) in the Cottrell plots. When the chronoamperometry was performed at various potentials of normal pulse voltammetry, the electron transfer numbers could be obtained at each potential [11–15]. In this paper, multiferrocenyl derivatives FcC(CH3)2Fc0 –C„C–Fc (A) (see Scheme 1) were synthesized and characterized by FT-IR, * Corresponding author. Tel.: +86 471 6575675; fax: +86 471 6575796. E-mail addresses: [email protected], [email protected] (L.-M. Han). 1387-7003/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2008.04.017
NMR, MS and element analysis [16,17], and the molecular structure of A was confirmed by single-crystal X-ray analysis [18], and FcC(CH3)2Fc0 –C„C–C„C–Fc0 C(CH3)2Fc (B) was synthesized according to the documental methods [19]. All manipulations were performed under a dry argon atmosphere using conventional Schlenk techniques, reagents of FcC(CH3)2Fc0 –C„CH, FcI, FcC(CH3)2Fc0 –C„CCu were synthesized according to the literatures and solvents were purified, dried and distilled under argon atmosphere prior to be used [20,21] (Fig. 1). According to the documental methods, the Cottrell plot (I vs. t1/2) at a microelectrode gives out s and p, where s ¼ p1=2 nD1=2 Fa2 c ð1 þ e1 Þ1 ; p ¼ pnFDac ð1 þ e1 Þ1 ; 1 ¼ ðF=RTÞðE E0 Þ. The electron transfer number can be obtained from n ¼ s2 =pFa3 c ð1 þ e1 Þ1 [22–24]. In order to confirm the validity of this method, the cyclic voltammetric and chronoamperometric properties of ferrocene were investigated with a microelectrode (d = 0.025 mm). The cyclic voltammograms showed that redox peaks of ferrocene theoretically disappeared with decreasing of scan rate (see Fig. 2) [24]. In the time domain from 0.1 to 10 s, the chronoamperometry was carried out by the potential stepping from 0.2 to 0.4, 0.2, 0.1, 0.0 V, respectively. The Cottrell plots were close to a linear relation in the time domain from 0.3 to 3.0 s while the background current was subtracted (see Fig. 3). On the assumption of 1 ! 1, we can calculate the s and p values by the formulas, then the electron transfer numbers were finally obtained by, n ¼ s2 =pFa3 c ð1 þ e1 Þ1 , which near to the theoretic value 1 (see Fig. 2) [23]. Therefore, this method was available for the determination of electron transfer number of ferrocenyl derivatives.
874
L.-M. Han et al. / Inorganic Chemistry Communications 11 (2008) 873–875
-e
a
b
-e
-e
FcC(CH3)2Fc'C2Fc
FcC(CH3)2Fc'C2Fc
FcC(CH3)2Fc'C2Fc
c
FcC(CH3)2Fc'C2Fc
A -2e
FcC(CH3)2Fc'C4Fc'(CH3)2CFc
a'
b'
c'
FcC(CH3)2Fc'C4Fc'(CH3)2CFc
d'
-e -e FcC(CH3)2Fc'C4Fc'(CH3)2CFc
FcC(CH3)2Fc'C4Fc'(CH3)2CFc
B Scheme 1. Redox processes of compounds A and B.
Fig. 1. Molecular structure of compound A and it is selected bond lengths [Å] and angles [°], C(10)–C(11) 1.508, C(11)–C(14) 1.537, C(16)–C(17) 1.428, C(17)–(C24) 1.448, (C24)–C(25) 1.208, C(25)–C(26) 1.428; C(10)–C(11)–C(12) 110.6, C(16)–C(17)–C(24) 126.6, C(24)–C(25)–C(26) 177.2, C(10)–C(11)–C(14) 106.5, C(17)–C(24)–C(25) 179.7, C(25)–C(26)–C(27) 126.7.
[×10 -7 ]
0.1
I/A
1
0
0
a
I / μA
n ( 1+e-ξ)-1
1
b c d
0 0
-0.2
0
0.2
0.4
E / V vs SCE Fig. 2. Cyclic voltammogram of 2.0 mM ferrocene + 0.2 M TBAP in acetonitrile and THF(v:v 10:1) at scan rate of 1 V s1 and 0.01 V s1 in the left ordinate. Values of nð1 þ e1 Þ1 (O in the right ordinate) obtained from the Cottrell plot.
The electron transfer numbers of compounds A and B were evaluated by the above method. The cyclic voltammograms of compounds A and B were shown in Fig. 4, both of them exhibited three well-defined waves, and the redox processes were deduced in Scheme 1. For compound A, since the bridged isopropyl carbon atom linked ferrocenyl unit a and b is an electron donor, the first oxidation should be ascribed to the ferrocenyl unit a, the second oxidation should be ascribed to the ferrocenyl unit b and the third oxidation come from ferrocenyl unit c. The higher oxidation potential of ferrocenyl unit c may be originated from the combination of the withdrawing electron function of alkynyl group and ferrocenium formed in second oxidative step, and all oxidations are one step one electron process. The potential difference between ferrocenyl unit b and c is about 130 mV, which consist
1 -1/2
t
2 -1/2
/s
Fig. 3. Cottrell plots of the background-sunstracted currents for 2.0 mM ferrocene + 0.2 M TBAP in acetonitrile and THF(v:v 10:1) when potential was stepped from (a) 0.2 to 0.4 V, (b) 0.2 to 0.2 V, (c) 0.2 to 0.1 V, (d) 0.2 to 0.0 V.
with the literature [25]. For compound B, ferrocenyl unit a0 and d0 are symmetric and non-conjugated, therefore, the first oxidation step maybe occurrs on this two ferrocenyl units, and it is one step two electron process. The second oxidation may come from the conjugated ferrocenyl unit b0 or c0 , if it comes from ferrocenyl unit b0 , the third oxidation should occur on ferrocenyl unit c0 , and each of them is one step one electron process. The potential difference of ferrocenyl unit b0 and c0 is about 100 mV, which is also consistent with the literature [25]. In order to identify the assumption of electron transfer processes in cyclic voltammetry, the chronoamperometry of compounds A and B were performed by stepping potentials from 0.2 to 0.1, 0.1 to 0.3 and 0.3 to 0.6 V, similar to that of ferrocene at a microelectrode (see Fig. 2). The Cottrell plots of the background-subtracted current of compound A were shown in Fig. 5,
L.-M. Han et al. / Inorganic Chemistry Communications 11 (2008) 873–875
875
method to determine the electron transfer numbers of multiferrocenyl derivatives.
B
I / μA
4 A
Acknowledgements
2 We are grateful to the Specialized Research Fund for the Doctoral Program of Higher Education of China (20060128001), the Natural Science Fund of Inner Mongolia (200711020201) and Specialized Research Fund of Inner Mongolia University of Technology (ZD200704).
0 -2 0
0.2 0.4 E / V vs SCE
0.6 Appendix A. Supplementary material
Fig. 4. Cyclic voltammograms of 2.0 mM (A) and (B) +0.2 M TBAP in mixture of acetonitrile and THF (v:v 10:1) at scan rate of 100 mV s1.
CCDC 638454 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2008. 04.017.
0.1
I /μA
References
0
1
2
t
-1/2
/s
3
-1/2
Fig. 5. Cottrell plots of the background-sunstracted currents for 2.0 mM compound (A) +0.2 M TBAP in acetonitrile and THF (v:v 10:1) when potential was stepped from (a) 0.2 to 0.1 V, (b) 0.1 to 0.3 V, (c) 0.3 to 0.6 V.
2
I / μA
0.05
1 0 0 -0.2
0
0.2 0.4 0.6 E / V vs SCE
0.8
Fig. 6. Electron transfer number, n (O), obtained from the Cottrell plots (Fig. 5) in the right ordinate and the nearly steady state voltammogram of compound A at scan rate 0.01 V s1 in the left ordinate.
and all plots are close to linear in the time domain from 0.3 to 3 s. As the linearity was valid for determination of s and p, the electron transfer numbers can be obtained by s and p. For compound A, the average electron transfer number (represented by symbol ‘‘O”, see Fig. 6) of each steps is near to 1. Moreover, the same experiment was performed on compound B, results showed that the electron transfer numbers of the first steps is 2, and the number of the second and the third steps is 1. The results confirmed that our assumptions on electron transfer number of A and B in cyclic voltammetry are reasonable, and the chronoamperometric technique of microelectrode is an effective
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