Molecular mechanics calculations on imine and mixed-ligand systems of Co^III, Ni^II and Cu^II

Abstract

The force field for the cellular ligand field stabilisation energy/molecular mechanics (CLFSE/MM) method has been applied to 28 transition-metal complexes. Computed and experimental structures are compared for 12 ML_xCl_6-x species (M = Co^III or Ni^II; L = amine donor; x = 6 or 4), 12 MA_xB_6-x compounds (M = Ni^II or Cu^II; A = imine, B = amine; x = 6, 4 or 3), one five-co-ordinate copper(II) imine–amine complex and three four-co-ordinate copper(II) imine and imine–amine molecules. For π-bonding ligands a stronger donor interaction is associated with a larger positive value of the CLF e_π parameter but, due to the use of a crystal field type barycentre, the CLFSE actually goes up. The CLFSE thus has the wrong form for treating the π contributions to bond stretching and distance-dependent e_π parameters are inappropriate. However, the desired bond lengths can be obtained by modifying the Morse function and e_σ terms. The π contribution to the L–M–L angle bending operates in the correct sense but is small and can also be accommodated by altering the magnitude of e_σ. For asymmetric π interactions (e_πx ≠ e_πy) there is no effect on the M–L torsional potential for low-spin d 6, high-spin d 8 and d 9 configurations where the π-symmetry d orbitals are completely filled. Hence, only the σ-bonding contributions to the CLFSE are retained. This approach still gives good agreement with experimental structures, even for formally π-bonding ligands, with average root-mean-square errors in M–L lengths and L–M–L angles of about 0.02 Å and 3° for Co^III, Ni^II and four co-ordinate Cu^II, excluding [Cu(bipy)₂]²⁺ (bipy = 2,2′-bipyridyl), and about 0.05 Å and 4° respectively for six-co-ordinate Cu^II, excluding [Cu(terpy)₂]²⁺ (terpy = 2,2′∶6′,2″ -terpyridyl). The subtle interplay between the axial Ni–Cl and equatorial Ni–N distances in trans-[NiN₄Cl₂] macrocyclic species is reproduced for the first time by an MM-based approach. However, the model appears to give relatively poor agreement for [Cu(bipy)₂(NH₃)]²⁺, [Cu(terpy)₂]²⁺ and [Cu(bipy)₂]²⁺. For the five-co-ordinate complex this is due to the intrinsic plasticity of five-co-ordinate copper(II) species. The energy difference between the limiting trigonal-bipyramidal and square-pyramidal geometries is only a few kcal mol^-1. For [Cu(terpy)₂]²⁺ the limiting geometries of tetragonally elongated and compressed octahedra are also within a few kcal mol^-1 although the present set of parameters overestimates the ligand contribution and predicts a compressed geometry. The calculated structure of [Cu(bipy)₂]²⁺ is too flat but for four-co-ordinate species it is shown, using [CuCl₄]^2- as an example, that there are several ways to induce a tetrahedral distortion. The most satisfactory method is to include charges on Cu and the ligand donors whereupon the geometries of [CuCl₄]^2- and [Cu(bipy)₂]²⁺ distort to the required flattened tetrahedral structures.

References

1. V. J. Burton, R. J. Deeth, C. M. Kemp and P. J. Gilbert, J. Am. Chem. Soc., 1995, 117, 8407.
2. P. Comba and T. W. Hambley, Molecular Modelling of Inorganic Compounds, VCH, Weinheim, 1995.
3. P. V. Bernhardt and P. Comba, Inorg. Chem., 1992, 33, 2638.
4. P. V. Bernhardt, P. Comba, T. W. Hambley, S. S. Massoud and S. Stebler, Inorg. Chem., 1992, 31, 2644.
5. R. K. Adam, M. Antolovich, L. G. Brigden and L. F. Lindoy, J. Am. Chem. Soc., 1991, 113, 3346.
6. B. P. Hay, Coord. Chem. Rev., 1993, 126, 177.
7. P. Comba, T. W. Hambley and L. Zipper, Helv. Chim. Acta, 1988, 71, 1875.
8. T. W. Hambley, Inorg. Chem., 1988, 27, 1073.
9. T. W. Hambley, J. Chem. Soc., Dalton Trans., 1986, 565.
10. T. W. Hambley, C. J. Hawkins, J. A. Palmer and M. R. Snow, Aust. J. Chem., 1991, 34, 45.
11. R. D. Hancock, S. M. Dobson, A. Evers, P. W. Wade, M. P. Ngwenya and J. C. A. Boeyens, J. Am. Chem. Soc., 1988, 110, 2788.
12. V. J. Burton and R. J. Deeth, J. Chem. Soc., Chem. Commun., 1995, 573.
13. M. Gerloch, Magnetism and Ligand Field Analysis, Cambridge University Press, New York, 1983.
14. M. Gerloch, J. H. Harding and R. G. Woolley, Struct. Bonding (Berlin), 1981, 46, 1.
15. Cambridge Structural Database, Version 4, Cambridge Crystallographic Data Centre, University Chemical Laboratory, Cambridge, 1994.
16. E. O. Schlemper, J. Cryst. Mol. Struct., 1977, 7, 81.
17. E. N. Duesler and K. N. Raymond, Inorg. Chem, 1971, 10, 1486.
18. R. Nagao, F. Marumo and Y. Saito, Acta Crystallogr., Sect. B, 1973, 29, 2438.
19. T. W. Hambley, G. H. Searle and M. R. Snow, Aust. J. Chem., 1982, 35, 1285.
20. K. Matsumoto, S. Ooi and H. Kuroya, Bull. Chem. Soc. Jpn., 1970, 43, 3801.
21. A. S. Foust and V. Janickis, Inorg. Chem., 1980, 19, 1048.
22. J. D. Mather, R. E. Tapscott and C. F. Campana, Inorg. Chim. Acta, 1983, 73, 235.
23. T. Ito and K. Toriumi, Acta Crystallogr., Sect. B, 1981, 37, 88.
24. T. Ito, M. Kato and H. Ito, Bull. Chem. Soc. Jpn., 1984, 57, 2641.
25. M. Sugimoto, J. Fugita, H. Ito, K. Toriumi and T. Ito, Inorg. Chem., 1983, 22, 955.
26. A. A. Watson, D. A. House and P. J. Steel, Inorg. Chim. Acta, 1987, 130, 167.
27. J. P. Konopelski, C. W. Reimann, C. R. Hubbard, A. D. Mighell and A. Santoro, Acta Crystallogr., Sect. B, 1976, 32, 2911.
28. A. Wada, N. Sakabe and J. Tanaka, Acta Crystallogr., Sect. B., 1976, 32, 1121.
29. M. I. Arriortua, T. Rojo, J. M. Amigo, G. Germain and J. P. Declercq, Bull. Soc. Chim. Belg., 1982, 91, 337.
30. P. V. Bernhardt, P. Comba, A. Mahu-Rickenbach, S. Stebler, S. Steiner, K. Varnagy and M. Zehnder, Inorg. Chem., 1992, 31, 4194.
31. C. W. Reinann, A. Santoro and A. D. Mighell, Acta Crystallogr., Sect. B, 1970, 26, 521.
32. A. W. Maverick, M. L. Ivie and F. R. Fronczek, J. Coord. Chem., 1990, 21, 315.
33. P. V. Bernhardt, P. Comba, A. Mahu-Rickenbach, S. Stebler, S. Steiner, K. Varnagy and M. Zehnder, Inorg. Chem., 1992, 31, 4194.
34. O. P. Anderson, J. Chem. Soc., Dalton Trans., 1972, 2597.
35. T. Astley, J. M. Gulbis, M. A. Hitchman and E. R. T. Tiekink, J. Chem. Soc., Dalton Trans., 1993, 509.
36. D. L. McFadden, A. T. McPhail, C. D. Garner and F. E. Mabbs, J. Chem. Soc., Dalton Trans., 1975, 263.
37. J. V. Folgado, W. Henke, R. Allmann, H. Stratmeier, D. Beltran-Porter, T. Rojo and D. Reinen, Inorg. Chem., 1990, 29, 2035.
38. F. S. Stephens, J. Chem. Soc., Dalton Trans., 1972, 1350.
39. G. Fransson and B. K. S. Lundberg, Acta Chem. Scand., 1972, 26, 3969.
40. D. L. Lewis and D. J. Hodgson, Inorg. Chem., 1974, 13, 143.
41. H. Nakai, Bull. Chem. Soc. Jpn., 1971, 44, 2412.
42. R. D. Hancock, Prog. Inorg. Chem., 1989, 37, 187.
43. T. Ito, M. Kato and H. Ito, Bull. Chem. Soc. Jpn., 1984, 57, 1556.
44. P. B. Hitchcock, K. R. Seddon and T. Welton, J. Chem. Soc., Dalton Trans., 1993, 2639.
45. R. Allmann, W. Henke and D. Reinen, Inorg. Chem., 1978, 17, 378.
46. R. J. Deeth and M. A. Hitchman, Inorg. Chem., 1986, 25, 1225.
47. W. D. Harrison, D. M. Kennedy, M. Power, R. Sheahen and B. J. Hathaway, J. Chem. Soc., 1963, 1556.
48. G. A. Barely, B. F. Hoskins and C. H. C. Kennard, J. Chem. Soc., 1963, 5691.
49. K. E. Halvarson, C. Patterson and R. D. Willett, Acta Crystallogr., Sect. B, 1990, 46, 508.
50. P. D. Sheen, Ph.D. Thesis, 1995, Bath University; K. Waizumi, H. Masuda, H. Einaga and N. Fukushima, Chem. Lett., 1993, 1145.