Stable mononuclear rhodium(II) polypyridyl complexes: synthesis, spectroscopic and structural characterisation

Abstract

The reaction of RhCl₃·3H₂O and 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) in refluxing ethanol–water (1∶1) resulted in the hydrolysis of tptz to bis(2-pyridylcarbonyl)amide anion (bpca) and afforded a mixture of Rh^III and Rh^II complexes which were separated and characterised as [Rh^III(bpca)₂][PF₆] and [Rh^II(bpca)₂]·3H₂O 1. Similarly the reaction of tptz and Rh(tpy)Cl₃ (tpy = 2,2′∶6′,2″-terpyridyl) yielded mixed ligand complexes [Rh^III(bpca)(tpy)]²⁺ and [Rh^Ii(bpca)(tpy)]Cl·8H₂O 2. The molecular structures of complexes 1 and 2 have been established by single-crystal X-ray analysis. In complex 1 two bpca moieties are co-ordinated to Rh^II with nitrogen as donor atoms in a mutually perpendicular fashion. In complex 2 bpca and tpy are bound to the metal ion in a similar fashion to that found in 1. The axial Rh–N bond distances in 1 and 2 are significantly shorter compared to equatorial Rh–N bond distances, indicating an axially compressed octahedral geometry of the metal ion. Complexes 1 and 2 exhibit absorption bands in the 545–600 nm region whereas their Rh^III analogues do not show any band in this region. Electrochemical studies of 1 and 2 revealed a metal based reduction (Rh^II→Rh^I) at –1.13 and –0.72 V, respectively, followed by two ligand-based redox couples. EPR studies of 1 and 2 in acetonitrile at 77 K show g_|| > g_⊥ ≈ g_e indicating a d_{x² – y²} ground state and a compressed octahedral geometry for the metal ion, consistent with the crystal structures.

References

1. T. R. Felthouse, Prog. Inorg. Chem., 1982, 29, 73.
2. E. B. Boyar and S. D. Robinson, Coord. Chem. Rev., 1983, 50, 109.
3. F. P. Pruchnik, Pure Appl. Chem., 1989, 61, 795.
4. L. Natkaniec and F. P. Pruchnik, J. Chem. Soc., Dalton Trans., 1994, 3261.
5. F. P. Pruchnik, F. Robert, Y. Jeannin and S. Jeannin, Inorg. Chem., 1996, 35, 4261.
6. K. K. Pandey, Coord. Chem. Rev., 1992, 121, 1.
7. D. G. DeWit, Coord. Chem. Rev., 1996, 147, 209.
8. N. G. Connelly, D. J. H. Emslie, B. Metz, A. G. Orpen and M. J. Quayle, Chem. Commun., 1996, 2289.
9. C. A. Ogle, T. C. Masterman and J. L. Hubbard, J. Chem. Soc., Chem. Commun., 1990, 1733.
10. S. C. Haefner, K. R. Dunbar and C. Bender, J. Am. Chem. Soc., 1991, 113, 9540.
11. K. R. Dunbar and S. C. Haefner, Organometallics, 1992, 11, 1431.
12. R. L. Harlow, D. L. Thorn, R. T. Baker and N. L. Jones, Inorg. Chem., 1992, 31, 993.
13. R. S. Hay-Motherwell, S. U. Koschmieder, G. Wilkinson, B. Hussain-Bates and M. B. Hursthouse, J. Chem. Soc., Dalton Trans., 1991, 2821.
14. M. P. Garcia, M. V. Jimenez, L. A. Oro, F. J. Lahoz, J. M. Casas and P. J. Alonso, Organometallics, 1993, 12, 3257.
15. S. Peng, Inorg. Chim. Acta, 1985, 101, L35.
16. K. R. Dunbar and S. C. Haefner, Inorg. Chem., 1992, 31, 3676.
17. T. Glowiak, H. Pasternak and F. Pruchnik, Acta Crystallogr., Sect. C, 1987, 43, 1036.
18. B. Martin, W. R. McWhinnie and G. M. Waind, J. Inorg. Nucl. Chem., 1961, 23, 207.
19. G. M. Brown, S. F. Chan, C. Creutz, H. A. Schwartz and N. Sutin, J. Am. Chem. Soc., 1979, 101, 7638.
20. Q. G. Mulazzani, S. Emmi, M. Z. Hoffman and M. Venturi, J. Am. Chem. Soc., 1981, 103, 3362.
21. H. A. Schwarz and C. Creutz, Inorg. Chem., 1983, 22, 707.
22. G. Kew, K. DeArmond and K. Hanck, J. Phys. Chem., 1974, 78, 727.
23. G. Kew, K. Hanck and K. DeArmond, J. Phys. Chem, 1975, 79, 1828.
24. P. Paul, B. Tyagi, M. M. Bhadbhade and E. Suresh, J. Chem. Soc., Dalton Trans., 1997, 2273.
25. P. Paul, B. Tyagi, A. K. Bilakhiya, M. M. Bhadbhade, E. Suresh and G. Ramachandraiah, Inorg. Chem., 1998, 37, 5733.
26. E. I. Gabe, Y. LePage, I. P. Charland, F. L. Lee and P. S. White, J. Appl. Crystallogr., 1989, 22, 384.
27. G. M. Sheldrick, Acta. Crystallogr., Sect. A, 1990, 46, 467.
28. G. M. Sheldrick, SHELXL 97, Program for refinement of crystal structures, University of Göttingen, 1997.
29. I. Vickovic, Crystal Structure Utility (CSU), a highly automated program for the calculation of geometrical parameters in the crystal structure analysis, Faculty of Science, University of Zagreb, Yugoslavia, 1988.
30. B. R. James and D. V. Stynes, J. Am. Chem. Soc., 1972, 94, 6225.
31. C. K. Johnson, ORTEP II, Report ORNL-5138, Oak Ridge National Laboratory, TN, 1976.
32. G. R. Desiraju, Acc. Chem. Res., 1991, 24, 290; Angew. Chem., Int. Ed. Engl., 1995, 34, 2311.
33. S. M. Peng, K. Peters, E. M. Peters and A. Simon, Inorg. Chim Acta, 1985, 101, L35.
34. G. P. Kakis and P. Saroulis, Inorg. Chim. Acta, 1980, 46, 97.
35. S. C. Rasmussen, M. M. Richter, E. Yi, H. Place and K. J. Brewer, Inorg. Chem., 1990, 29, 3926.
36. J. A. Osborn, F. J. Jardine, J. F. Young and G. Wilkinson, J. Chem. Soc. A, 1966, 1711.
37. M. C. Baird, Inorg. Chim Acta, 1971, 5, 46.
38. M. D. Sastry, K. Savitri and B. D. Joshi, J. Chem. Phys., 1980, 73, 5568.
39. G. C. Abell and R. C. Bowman, Jr., J. Chem. Phys., 1979, 70, 2611.
40. D. Goldfarb and L. Kevan, J. Phys. Chem., 1986, 90, 264, 2137 and 5787.
41. C. Bianchini, P. Frediani, F. Laschi, A. Meli, F. Vizza and P. Zonello, Inorg. Chem., 1990, 29, 3402.