The shapes of bis(cyclopentadienyl) complexes of the s-block metals

Abstract

The structures and bonding of the bis(cyclopentadienyl) complexes of the alkaline-earth metals and the alkali metals have been studied using density functional calculations within the linear combination of Gaussian-type orbitals framework. The compounds Ca(cp)₂ and Sr(cp)₂ are predicted to have bent equilibrium structures in agreement with the experimentally determined shapes but in contrast to previous theoretical investigations; Mg(cp)₂ and the isoelectronic [M(cp)₂]^- (M = Li, Na, K or Rb) ions are predicted to have coparallel, staggered rings. Analysis of the bonding shows that π-type interactions dominate for the complexes of the heavier metals of both groups as a result of the increased influence of the metal d functions. Their role is key to the driving force for the bent geometries of Ca(cp)₂ and Sr(cp)₂ just as it is for the anomalous shapes of some of the dihalide molecules. The key orbital interaction, however, is quite different.

References

1. (a) R. A. Anderson, J. M. Boncella, C. J. Burns, R. Blom, A. Haaland and H. V. Volden, J. Organomet. Chem., 1986, 312, C49; (b) R. A. Anderson, R. Blom, J. M. Boncella, C. J. Burns and H. V. Volden, Acta Chem. Scand., Ser. A, 1987, 41, 24; (c) R. A. Anderson, R. Blom, J. M. Boncella, C. J. Burns and H. V. Volden, J. Chem. Soc. Chem. Commun., 1987, 768; (d) R. Blom, K. Faegri, jun. and H. V. Volden, Organometallics, 1990, 9, 372.
2. (a) R. A. Williams, T. P. Hanusa and J. C. Huffman, J. Chem. Soc., Chem. Commun., 1988, 1045; (b) Organometallics, 1990, 9, 1128.
3. W. Bunder and E. Weiss, J. Organomet. Chem., 1975, 92, 1.
4. M. Kaupp, P. v. R. Schleyer, M. Dolg and H. Stoll, J. Am. Chem. Soc., 1992, 114, 8202.
5. M. Hargittai, Coord. Chem. Rev., 1988, 91, 35 and refs. therein.
6. (a) E. F. Hayes, J. Phys. Chem., 1966, 70, 3740; (b) D. R. Yarkonyi, W. J. Hunt and H. F. Schäffer, Mol. Phys., 1973, 26, 941; (c) J. L. Gole, A. K. Q. Siu and E. F. Hayes, J. Chem. Phys., 1973, 58, 857; (d) M. Guido and G. Gigli, J. Chem. Phys., 1974, 61, 4138; (e) M. Guido and G. Gigli, J. Chem. Phys., 1976, 65, 1397; (f) D. M. Hassett and C. J. Marsden, J. Chem. Soc. Chem. Commun., 1990, 667; (g) J. M. Dyke and T. G. Wright, Chem. Phys. Lett., 1990, 169, 138; (h) L. v. Szentpály and P. Schwerdtfeger, Chem. Phys. Lett., 1990, 170, 555; (i) U. Salzner and P. v. R. Schleyer, Chem. Phys. Lett., 1990, 172, 461; (j) R. L. DeKock, M. A. Peterson, L. K. Timmer, E. J. Baerends and P. Vernooijs, Polyhedron, 1990, 9, 1919; (k) M. Kaupp and P. v. R. Schleyer, J. Chem. Phys., 1991, 94, 1360; (l) L. Seijo, Z. Barandiarán and S. Huzinaga, J. Chem. Phys., 1991, 94, 3762; (m) M. Kaupp and P. v. R. Schleyer, J. Am. Chem. Soc., 1992, 114, 491; (n) I. Bytheway, R. J. Gillespie, T.-H. Tang and R. F. W. Bader, Inorg. Chem., 1995, 34, 2407.
7. W. J. Evans, L. S. Hughes and T. P. Hanusa, Organometallics, 1986, 5, 1285.
8. J. K. Burdett, in Accurate Molecular Structures: Their Determination and Importance, eds. A. Domenicano and I. Hargittai, Oxford University Press, Oxford, 1992; T. K. Hollis, J. K. Burdett and B. Bosnich, Organometallics, 1993, 12, 3385.
9. Local Density Approximations in Quantum Chemistry and Solid-State Physics, eds. J. P. Dahl and J. Avery, Plenum, New York, 1989.
10. R. G. Parr and W. Yang, Density-Functional Theory of Atoms and Molecules, Oxford University Press, Oxford, 1989.
11. Density Functional Methods in Chemistry, eds. J. K. Labanowski and J. W. Andelm, Springer, New York, 1991.
12. T. Ziegler, Chem. Rev., 1991, 91, 651.
13. J. Thiele, Dtsch. Chem. Ges., 1901, 34, 68.
14. S. Harder and M. H. Prosenc, Angew. Chem., Int. Ed. Engl., 1994, 33, 1744.
15. D. Stalke, Angew. Chem., Int. Ed. Engl., 1994, 33, 2168.
16. S. Harder, M. H. Prosenc and U. Rief, Organometallics, 1996, 15, 118.
17. A. St-Amant, DEFT, a FORTRAN program, University of Ottawa, 1994.
18. S. H. Vosko, L. Wilk and M. Nusair, Can. J. Phys., 1980, 58, 1200.
19. A. D. Becke, Phys. Rev. A, 1988, 38, 3098.
20. J. P. Perdew, Phys. Rev. B, 1986, 33, 8822.
21. N. Godbout, D. R. Salahub, J. Andzelm and E. Wimmer, Can. J. Chem., 1992, 70, 1992.
22. Gaussian Basis Sets for Molecular Calculations, ed. S. Huzinaga, Elsevier, New York, 1984.
23. I. Mayer, Chem. Phys. Lett., 1983, 97, 270.
24. I. Mayer, Int. J. Quantum Chem., 1984, 26, 151.
25. F. A. Cotton, Chemical Applications of Group Theory, Wiley-Interscience, New York, 1990.
26. S. Evans, M. L. H. Green, B. Jewitt, A. F. Orchard and C. F. Pygall, J. Chem. Soc., Faraday Trans. 2, 1972, 1847.
27. J. S. Slater, The Calculation of Molecular Orbitals, Wiley-Interscience, New York, 1979.
28. Comprehensive Organometallic Chemistry, ed. G. Wilkinson, Pergamon, New York, 1982.
29. P. Jutzi, F. Kohl, P. Hoffman, C. Krüger and Y.-H. Tsay, Chem. Ber., 1980, 113, 757; J. L. Atwood, W. E. Hunter, A. H. Cowley, R. A. Jones and C. A. Stewart, J. Chem. Soc. Chem. Commun., 1981, 925; M. Grenz, E. Hahn, W.-W. du Mont and J. Pickardt, Angew. Chem., Int. Ed. Engl., 1984, 23, 61; P. Jutzi, D. Kanne and C. Krüger, Angew. Chem., Int. Ed. Engl., 1986, 25, 164.
30. D. J. Burkey and T. P. Hanusa, Comments Inorg. Chem., 1995, 17, 41.
31. C. Panattoni, G. Bombieri and U. Croato, Acta. Crystallogr., 1966, 21, 823.
32. I. R. Beattie, J. S. Ogden and R. S. Wyatt, J. Chem. Soc., Dalton Trans., 1983, 2343.
33. N. N. Greenwood and A. Earnshaw, Chemistry of the Elements, Pergamon, Oxford, 1986.