View PDF Version
 
DOI: 10.1039/A903560E (Paper) Reference Section for: J. Chem. Soc., Dalton Trans., 1999, 3081-3086

Structural and electronic changes accompanying reduction of Cr(CO)4(bpy) to its radical anion: a quantum chemical interpretation of spectroelectrochemical experiments

(Note: The full text of this document is currently only available in the PDF Version )

Stanislav Záliš, Chantal Daniel, Antonín Vlček and Chantal Daniel, Antonín Vlček, Jr.

Abstract

Optimised molecular structures and charge distributions within Cr(CO)4(bpy) and its radical anion were calculated using density functional theory (DFT). It was found that, although reduction predominantly concerns the bpy ligand, its structural and electronic effects extend to the Cr(CO)4 fragment. Each equatorial and axial CO ligand was calculated to accept 7.1 and 4.8%, respectively, of the extra electron density in Cr(CO)4(bpy)˙–. This is in accordance with the IR spectroelectrochemical results which show that the corresponding CO stretching force constants decrease by 68 and 21 N m–1, respectively. The calculated spin density in Cr(CO)4(bpy)˙– resides predominantly on the bpy ligand which behaves spectroscopically as bpy˙–. The spin density is delocalised to both axial and equatorial pairs of CO ligands by mixing of π*(C[triple bond, length half m-dash]O) orbitals with the, predominantly π*(bpy), SOMO. In addition, part of the spin density is delocalised selectively to the axial CO ligands by an admixture of their σ orbitals into the SOMO. This σ–π* contribution is responsible for isotropic EPR hyperfine splitting which was observed from the axial 13C(CO) atoms only. Accordingly, the isotropic hyperfine splitting constants correlate with calculated Fermi contact terms instead of total spin densities. Complete active space self-consistent field (CASSCF)-calculated changes in charge distribution upon a Cr→bpy MLCT excitation show that the electron density localised on the bpy ligand increases by about the same amount upon reduction or MLCT-excitation of Cr(CO)4(bpy). The axial CO ligands are depopulated by MLCT excitation ca. 1.6 times more than the equatorial ones. These conclusions can be generalised and applied to other coordination and organometallic complexes of low-valent metals which contain a reducible or radical-anionic ligand.

References

  1. D. J. Stufkens, Coord. Chem. Rev., 1990, 104, 39 CrossRef CAS.
  2. R. W. Balk, T. Snoeck, D. J. Stufkens and A. Oskam, Inorg. Chem., 1980, 19, 3015 CrossRef CAS.
  3. J. Víchová, F. Hartl and A. Vlček, Jr., J. Am. Chem. Soc., 1992, 114, 10903 CrossRef CAS.
  4. A. Vlček, Jr., J. Víchová and F. Hartl, Coord. Chem. Rev., 1994, 132, 167 CrossRef.
  5. I. G. Virrels, M. W. George, J. J. Turner, J. Peters and A. Vlček, Jr., Organometallics, 1996, 15, 4089 CrossRef CAS.
  6. D. Guillaumont, C. Daniel and A. Vlček, Jr., Inorg. Chem., 1997, 36, 1684 CrossRef CAS.
  7. I. R. Farrell, P. Matousek and A. Vlček, Jr., J. Am. Chem. Soc., 1999, 121, 5296 CrossRef.
  8. D. Miholova and A. A. Vlček, J. Organomet. Chem., 1985, 279, 317 CrossRef CAS.
  9. A. Vlček, Jr., F. Baumann, W. Kaim, F.-W. Grevels and F. Hartl, J. Chem. Soc., Dalton Trans., 1998, 215 RSC.
  10. A. Vlček, Jr., F.-W. Grevels, T. L. Snoeck and D. J. Stufkens, Inorg. Chim. Acta, 1998, 278, 83 CrossRef.
  11. D. Guillaumont, C. Daniel and A. Vlček, Jr., manuscript in preparation.
  12. S. Wieland, K. B. Reddy and R. van Eldik, Organometallics, 1990, 9, 1802 CrossRef CAS.
  13. W.-F. Fu and R. van Eldik, Inorg. Chem., 1998, 37, 1044 CrossRef CAS.
  14. W. F. Fu and R. van Eldik, Inorg. Chim. Acta, 1996, 251, 341 CrossRef.
  15. H. Kobayashi, Y. Kaizu, H. Kimura, H. Matsuzawa and H. Adachi, Mol. Phys., 1988, 64, 1009 CAS.
  16. A. Vlček, Jr., Chemtracts–Inorg. Chem., 1993, 5, 1 Search PubMed.
  17. M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. Montgomery, Jr., R. E. Stratmann, J. C. Burant, S. Dapprich, J. M. Millam, A. D. Daniels, K. N. Kudin, M. C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui, K. Morokuma, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. Cioslowski, J. V. Ortiz, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, C. Gonzalez, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, J. L. Andres, C. Gonzalez, M. Head-Gordon, E. S. Replogle and J. A. Pople, Gaussian 98, Revision A.6, Gaussian, Inc., Pittsburgh, PA, 1998.
  18. K. Andersson, M. R. A. Blomberg, M. P. Flüscher, G. Karström, V. Kellö, R. Lindh, P.-Å. Malmqvist, J. Noga, J. Olsen, B. O. Roos, A. J. Sadlej, P. E. M. Siegbahn, M. Urban and P.-O. Widmark, MOLCAS version 3.0, University of Lund, Sweden, 1994.
  19. A. D. Becke, J. Chem. Phys., 1993, 98, 5648 CrossRef CAS.
  20. N. Godbout, D. R. Salahub, J. Andzelm and E. Wimmer, Can. J. Chem., 1992, 70, 560 CAS.
  21. T. H. Dunnning and P. J. Hay, in Modern Theoretical Chemistry, ed. H. F. Schaefer, III, Plenum, New York, 1976 Search PubMed.
  22. C. Adamo and V. Barone, Chem. Phys. Lett., 1997, 274, 242 CrossRef CAS.
  23. W. J. Hehre, R. Ditchfield and J. A. Pople, J. Chem. Phys., 1972, 56, 2257 CrossRef CAS.
  24. T. Clark, J. Chandrasekhar and P. v. R. Schleyer, J. Comput. Chem., 1983, 4, 294 CrossRef CAS.
  25. H. Saito, J. Fujita and K. Saito, Bull. Chem. Soc. Jpn., 1968, 41, 863 CAS.
  26. H. Saito, J. Fujita and K. Saito, Bull. Chem. Soc. Jpn., 1968, 41, 359 CAS.
  27. B. A. Goodman and J. B. Raynor, Adv. Inorg. Chem. Radiochem., 1970, 13, 135 CAS.
  28. M. Symons, Chemical and Biochemical Aspects of Electron-Spin Resonance Spectroscopy, Van Nostrand Reinhold Company Ltd., Wokingham, England, 1978 Search PubMed.
  29. J. E. Wertz and J. R. Bolton, Electron Spin Resonance. Elementary Theory and Practical Applications, Chapman and Hall, New York, 1986 Search PubMed.
  30. W. Kaim, Coord. Chem. Rev., 1987, 76, 187 CrossRef CAS.
  31. W. Kaim and S. Kohlmann, Inorg. Chem., 1990, 29, 2909 CrossRef CAS.
  32. W. Kaim, Inorg. Chem., 1984, 23, 3365 CrossRef CAS.
  33. A. Klein, C. Vogler and W. Kaim, Organometallics, 1996, 15, 236 CrossRef CAS.
  34. F. Hartl and A. Vlček, Jr., Inorg. Chem., 1996, 35, 1257 CrossRef CAS.
  35. W. Kaim, B. Olbrich-Deussner, R. Gross, S. Ernst, S. Kohlmann and C. Bessenbacher, in Importance of Paramagnetic Organometallic Species in Activation, Selectivity and Catalysis, eds. M. Chanon, M. Julliard and J.-C. Poite, Kluwer Academic Publishers, Dordrecht, The Netherlands, 1989 Search PubMed.
  36. M. P. Aarnts, D. J. Stufkens, M. P. Wilms, E. J. Baerends, A. Vlček, Jr., I. P. Clark, M. W. George and J. J. Turner, Chem. Eur. J., 1996, 2, 1556 CAS.
  37. M. P. Aarnts, M. P. Wilms, K. Peelen, J. Fraanje, K. Goubitz, F. Hartl, D. J. Stufkens, E. J. Baerends and A. Vlček, Jr., Inorg. Chem., 1996, 35, 5468 CrossRef CAS.
  38. W. Kaim, A. Klein, S. Hasenzahl, H. Stoll, S. Záliš and J. Fiedler, Organometallics, 1998, 17, 237 CrossRef CAS.
  39. S. Hasenzahl, H.-D. Hausen and W. Kaim, Chem. Eur. J., 1995, 1, 95 CAS.
  40. B. S. Brunschwig, C. Creutz and N. Sutin, Coord. Chem. Rev., 1998, 177, 61 CrossRef CAS.
Click here to see how this site uses Cookies. View our privacy policy here.