Lead complexation by novel phenanthroline-containing macrocycles †

Abstract

Two new polyamine macrocycles 2,5,8-triaza[9]-[9](2,9)[1,10]-phenanthrolinophane (L¹) and 2,5,8,11-tetraaza[12]-[12](2,9)[1,10]-phenanthrolinophane (L²) have been synthesized and characterized. They contain a triamine (L¹) or a tetraamine (L²) chain linking the 2,9 positions of a phenanthroline moiety. Like L³, which contains a pentaamine chain connecting the 2,9-phenanthroline positions, they form stable 1∶1 lead(II) complexes in aqueous solutions. These complexes can readily be extracted in non-aqueous solvents, such as CHCl₃ or CH₂Cl₂. The thermodynamic parameters for lead(II) complexation have been determined by means of potentiometric and microcalorimetric measurements in aqueous solutions. The stability of the complexes decreases from L¹ to L³ mainly due to a marked decrease of the enthalpy changes related to the formation of the complexes, indicating that the overall metal–ligand interaction decreases from L¹ to L³. Most likely, in the [PbL¹]²⁺ complex all donors are strongly involved in metal co-ordination, while in [PbL²]²⁺ and [PbL³]²⁺ some of the amine groups are weakly bound, or not bound, to the metal. These considerations are supported by the crystal structures of [(PbL¹Br)₂(µ-Br)][PbL¹Br₂]Br·5H₂O. In the latter complex the macrocycle wraps around the metal. On the other hand, three nitrogen donors interact at remarkably longer distance than the others. This observation may justify the lower stability of the [PbL³]²⁺ complex with respect to that of [PbL¹]²⁺.

References

1. M. N. Hughes, The Inorganic Chemistry of the Biological Processes, Wiley, New York, 1981.
2. (a) J. S. Bradshaw, Aza-crown Macrocycles, Wiley, New York, 1993; (b) R. M. Izatt, J. S. Bradshaw, S. A. Nielsen, J. D. Lamb, J. J. Christensen and D. Sen, Chem. Rev., 1985, 85, 271; (c) R. M. Izatt, K. Pawlak and J. S. Bradshaw, Chem. Rev., 1991, 91, 1721; (d) J. Nelson, V. McKee and G. Morgan, Prog. Inorg. Chem., 1998, 47, 167.
3. L. F. Lindoy, The Chemistry of Macrocyclic Ligand Complexes, Cambridge University Press, Cambridge, 1989; M. Dobler, Ionophores and their Structure, Wiley-Interscience, New York, 1981.
4. N. W. Alcock, E. W. Curzon and P. Moore, J. Chem. Soc., Dalton Trans., 1984, 605.
5. K. Wieghardt, M. Kleine-Boymann, B. Nuber, J. Weiss, L. Zsolnai and G. Huttner, Inorg. Chem., 1986, 25, 1647.
6. M. G. B. Drew, A. Rodgers, M. McCann and S. M. Nelson, J. Chem. Soc., Chem. Commun., 1978, 415.
7. (a) R. D. Hancock, M. S. Shaikjee, S. M. Dobson and C. A. Boeyens, Inorg. Chim. Acta, 1988, 154, 229; (b) V. J. Thöm, M. S. Shaikjee and R. D. Hancock, Inorg. Chem., 1986, 25, 2992; (c) V. J. Thöm, G. D. Hosken and R. D. Hancock, Inorg. Chem., 1985, 24, 3378; (d) V. J. Thöm and R. D. Hancock, J. Chem. Soc., Dalton Trans., 1985, 1877.
8. A. Bencini, A. Bianchi, E. Garcia-España, M. Micheloni and P. Paoletti, Inorg. Chem., 1988, 27, 186 and refs. therein A. Bencini, A. Bianchi, P. Paoletti and P. Paoli, Coord. Chem. Rev., 1992, 120, 51.
9. A. Andres, A. Bencini, A. Charachalios, A. Bianchi, P. Dapporto, E. Garcia-España, P. Paoletti and P. Paoli, J. Chem. Soc., Dalton Trans., 1993, 3507.
10. P. G. Sammes and G. Yahioglu, Chem. Soc. Rev., 1994, 328.
11. J. E. Richman and T. J. Atkins, J. Am. Chem. Soc., 1974, 96, 2268.
12. C. J. Chandler, L. W. Deady and J. A. Reiss, J. Heterocycl. Chem., 1981, 18, 599.
13. C. K. Johnson, ORTEP, Report ORNL-3794, Oak Ridge National Laboratory, Oak Ridge, TN, 1971.
14. K. Byriel, K. R. Dunster, L. R. Gahan, C. H. L. Kennard, J. L. Latten, I. L. Swann and P. A. Duckworth, Polyhedron, 1992, 10, 1205.
15. L. Shimoni-Livny, J. P. Glusker and C. W. Bock, Inorg. Chem., 1998, 37, 1853.
16. M. Kodama and E. Kimura, J. Chem. Soc., Dalton Trans., 1978, 1081; 19802536.
17. A. Bencini, A. Bianchi, E. Garcia-España, M. Giusti, M. Micheloni and P. Paoletti, Inorg. Chem., 1987, 26, 681.
18. C. Bazzicalupi, A. Bencini, V. Fusi, C. Giorgi, P. Paoletti and B. Valtancoli, Inorg. Chem., 1998, 37, 941.
19. DIFABS, N. Walker and D. D. Stuart, Acta Crystallogr., Sect. A, 1983, 39, 158; SHELX 76, G. M. Sheldrick, Program for Crystal Structure Determination, University of Cambridge, 1976; SHELXL 93, G. M. Sheldrick, University of Göttingen, 1993; International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974, vol. IV.
20. A. Bianchi, L. Bologni, P. Dapporto, M. Micheloni and P. Paoletti, Inorg. Chem., 1984, 23, 1201.
21. G. Gran, Analyst (London), 1952, 77, 661; F. J. Rossotti and H. Rossotti, J. Chem. Educ., 1965, 42, 375.
22. P. Gans, A. Sabatini and A. Vacca, J. Chem. Soc., Dalton Trans., 1985, 1195.
23. M. Micheloni, KK88 computer program (Fortran), University of Florence, 1995.