Electrochemistry and surface-enhanced Raman spectroscopy (SERS) of adsorbed chromium–bipyridyl complexes†

Abstract

A series of bis-bipyridyl complexes, cis-[Cr^III(bpy)₂(L)(L′)] (L = OH, L′ = OH₂ monomer; L = L = OH dimer; L = L = Cl; and L, L′ = polyacrylic acid) were studied at silver and glassy carbon electrodes by cyclic voltammetry. On reduction, slow electron transfer reactions giving adsorbed species are evident from the cyclic voltammograms. In situ surface-enhanced Raman spectroscopy (SERS) of the aquahydroxo and dimer complexes shows a broad, intense Cr–O vibration at around 550 cm^–1. This arises as the exciting line (514.5 nm) is close to resonance with the lowest energy absorption band assigned to a ligand field transition (⁴A_2g → ⁴T_2g). At –0.4 V SERS spectra show features of both the normal Raman spectrum of [Cr(bpy)₃]³⁺ and the colloidal SERS of [Cr(bpy)₃]²⁺ and can be explained by the presence of partially-reduced adsorbed species. The electron is localized first on to the metal and then on to one of the bpy ligands as follows: [Cr^III(bpy⁰)₂X₂]ⁿ⁺ + e →[Cr^II(bpy⁰)₂X₂]^(n–1)+ and [Cr^II(bpy⁰)₂X₂]^(n–1)+ + e →[Cr^II(bpy^–)(bpy⁰)₂X₂]^(n–2)+. Although the SERS evidence suggested that the integrity of the complexes is maintained during the reaction, prolonged electrolysis leads to hydrolysis and/or substitution of the complexes. Thus [(PVP)₂-Cr(bpy)₂]³⁺ can be electrosynthesized by reduction of cis-[Cr(bpy)Cl₂]⁺ at a PVP modified glassy carbon electrode and shows a characteristic peak at –0.32 V.

References

1. M. A. Jamieson, N. Serpone and M. Z. Hoffman, Coord. Chem. Rev., 1981, 39, 121.
2. M. Asano, D. Mongeau, D. Nicollin, R. Sasseville and J. A. Koningstein, Chem. Phys. Lett., 1979, 65, 293.
3. M. Asano, J. A. Koningstein and D. Nicollin, J. Chem. Phys., 1980, 73, 688.
4. K. Kniepp, H. Kniepp and E. Dinjus, Chem. Phys. Lett., 1986, 126, 69.
5. M. C. Hughes and D. J. Macero, Inorg. Chem., 1976, 15, 2040.
6. D. M. Soignet and L. G. Hargis, Inorg. Chem., 1972, 11, 2349.
7. S. D. Nadler, J. G. Dick and C. H. Langford, Can. J. Chem., 1985, 63, 2732.
8. (a) K. Nakano, Y. Narusawa and H. Moroi, Bull Chem. Soc. Jpn., 1981, 54, 2529; (b) K. Nakano, Y. Narusawa and M. Tsuchiya, J. Inorg. Nucl. Chem., 1981, 43, 3011.
9. (a) L. Jeftic and S. W. Feldberg, J. Phys. Chem., 1971, 75, 2381; (b) S. W. Feldberg and L. Jeftic, J. Phys. Chem., 1972, 76, 2439.
10. D. Astruc, Angew. Chem., Int. Ed. Engl., 1988, 27, 643.
11. D. H. Evans, Chem. Rev., 1990, 90, 739.
12. F. H. Burstall and R. S. Nyholm, J. Chem. Soc., 1952, 3570.
13. J. Ulstrup, Acta Chem. Scand., 1971, 25, 3397.
14. W. A. Wickramasinghe, P. H. Bird, M. A. Jamieson, N. Serpone and M. Maestri, Inorg. Chim. Acta, 1982, 64, L85.
15. M. Maestri, F. Bolletta, N. Serpone, L. Moggi and V. Balzani, Inorg. Chem., 1976, 15, 2048.
16. (a) R. G. Inskeep and J. Bjerrum, Acta Chem. Scand., 1961, 15, 62; (b) U. Castellato, R. Graziani, G. Maccarrone and A. J. di Billio, J. Crystallogr. Spectrosc. Res., 1986, 16, 695.
17. M. Ardon and A. Bino, Inorg. Chem., 1985, 24, 1343.
18. J. Josephsen and C. E. Schäffer, Chem. Commun, 1970, 60; Acta Chem. Scand., 1970, 24, 2929.
19. P. Andersen, Coord. Chem. Rev., 1989, 94, 47; J. Springborg, Adv. Inorg. Chem. Radiochem., 1988, 32, 55.
20. M. A. Billadeau and H. Morrison, J. Inorg. Biochem., 1995, 57, 249.
21. A. P. Taylor, J. A. Crayston and T. J. Dines, J. Chem. Soc., Faraday Trans., 1997, 93, 1803.
22. K. Anbalagan and P. Natarajan, J. Polym. Sci., Part A: Polym. Chem., 1991, 29, 1739.
23. H. Nishide, S. Hata and E. Tsuchida, Makromol. Chem., 1978, 179, 1445.
24. M. P. Hancock, J. Josephsen and C. E. Schäffer, Acta Chem. Scand., Ser. A, 1976, 30, 79.
25. W. Khamawphlang, S. Choudhury, A. K. Deb and S. Goswani, Inorg. Chem., 1995, 34, 3825.
26. D. T. Sawyer and J. L. Roberts, Jr., Experimental Electrochemistry for Chemists, Wiley, Chichester, 1974.
27. P. Corio and J. C. Rubim, J. Phys. Chem., 1995, 99, 13217.
28. R. S. Lawton and A. M. Yacynych, Anal. Chim. Acta, 1984, 160, 149.
29. P. G. Bradley, N. Kress, B. A. Hornberger, R. F. Dallinger and W. H. Woodruff, J. Am. Chem. Soc., 1981, 103, 7441.
30. M. Forster and R. E. Hester, Chem. Phys. Lett., 1981, 81, 42.
31. K. D. Sugden, R. D. Geer and S. J. Rogers, Biochemistry, 1992, 31, 11626.
32. A. Fitch, A. Lavy-Feder, S. A. Lee and M. T. Kirsh, J. Phys. Chem., 1988, 92, 6665.
33. B. V. Tucker, J. M. Fitzgerald, L. G. Hargis and L. B. Rogers, J. Electroanal. Chem., 1967, 13, 400.
34. G. A. Lawrence and D. F. Sangster, J. Chem. Soc., Dalton Trans., 1987, 1425.
35. D. G. Holah and J. P. Fackler, Inorg. Chem., 1965, 4, 1112.
36. R. Jiang and F. C. Anson, J. Phys. Chem., 1992, 96, 452.
37. D. Gourier, A. Tranchant, N. Baffier and R. Messina, ELectrochim. Acta, 1992, 37, 2755.
38. R. J. Fitzgerald, B. B. Hutchinson and K. Nakamoto, Inorg. Chem., 1970, 9, 2618.
39. G. N. La Mar and G. R. Van Hecke, Inorg. Chem., 1973, 12, 1767.
40. J. A. Chambers and R. P. Buck, J. Electroanal. Chem., 1984, 163, 297.
41. M. Kim and K. Itoh, J. Electroanal. Chem., 1985, 188, 137.