Lanthanide complexes of the tetradentate N-donor ligand dihydrobis[3-(2-pyridyl)pyrazolyl]borate and the terdentate N-donor ligand 2,6-bis(1H-pyrazol-3-yl)pyridine: syntheses, crystal structures and solution structures based on luminescence lifetime studies

Abstract

Lanthanide complexes of two polydentate N-donor ligands containing a mixture of pyridyl and pyrazolyl donors have been prepared. Dihydrobis[3-(2-pyridyl)pyrazolyl]borate (L¹)^- is a tetradentate ligand with two bidentate chelating pyridyl/pyrazolyl arms linked by an apical BH₂ group; 2,6-bis(1H-pyrazol-3-yl)pyridine (L²) is a terdentate chelating ligand reminiscent of terpyridine. Reaction of L¹ with lanthanide salts gave complexes of the type [M(L¹)₂X]ⁿ⁺; the crystal structures of [Eu(L¹)₂(dmf )][ClO₄]· 2.5CH₂Cl₂, [Tb(L¹)₂(NO₃)]·2CH₂ Cl₂ and [Tb(L¹)₂(H₂O)][L¹]· H₂O·0.5CH₂Cl₂ were determined and all contain two tetradentate ligands L¹ and an ancillary ligand X [dimethylformamide (dmf ), nitrate or water] whose nature depends on the reaction/recrystallisation conditions to complete the co-ordination sphere. Luminescence studies of [Tb(L¹)₂(NO₃)] in water or D₂O and MeOH or CD₃OD showed that in methanol the solvation number q is ≈1.8, consistent with displacement of nitrate by the solvent; however in water q ≈ 4.5, indicating additional displacement of some of the N-donor heterocyclic rings of L¹ by co-ordinating water molecules. Reaction of L² with lanthanide salts afforded [M(L²)₃]³⁺, all isolated as their hexafluorophosphate salts. The crystal structures of three of these (M = Eu, Gd or Ho) showed that they are isostructural and isomorphous, with tricapped trigonal-prismatic nine-co-ordinate geometries similar to that of [M(terpy)₃]³⁺ (terpy = 2,2′ : 6′,2″- terpyridine). Luminescence studies of [Tb(L²)₃][PF₆]₃ gave a solvation number q of 0.6 in methanol, which is small enough to be accounted for by second-sphere solvation effects alone and therefore suggests that the nine-co-ordinate structure is retained in methanol solution. However in water, q is again ≈4.5, due to displacement of some of the donor groups of the L² ligands by water.

References

1. E. Soini, I. Hemmilä and P. Dhalen, Ann. Biol. Chem., 1990, 48, 567; J.-C. G. Bünzli, in Lanthanide Probes in Life, Chemical and Earth Sciences, Theory and Practice, eds. J.-C. G. Bünzli and G. R. Choppin, Elsevier, Amsterdam, 1989, p. 219; A. K. Saha, K. Kross, E. D. Kloszewski, D. A. Upson, J. L. Toner, R. A. Snow, C. D. V. Black and V. C. Desai, J. Am. Chem. Soc., 1993, 115, 11 032; V. M. Mukkala, M. Heleniu, I. Hemmilä, J. Kankare and H. Takalo, Helv. Chim. Acta, 1993, 76, 1361; M. J. P. Leiner, Anal. Chim. Acta, 1991, 255, 209; A. P. de Silva, H. Q. N. Gunaratne and T. E. Rice, Angew. Chem., Int. Ed. Engl., 1996, 35, 2116; M. A. Mortellaro and D. G. Nocera, J. Am. Chem. Soc., 1996, 118, 7414.
2. S. H. Koenig and R. D. Brown, Prog. Nucl. Magn. Reson. Spectrosc., 1990, 22, 487; R. B. Lauffer, Chem. Rev., 1987, 87, 901; D. Parker, Chem. Br., 1994, 818; A. D. Watson, J. Alloys Compd., 1994, 207/208, 14; S. Aime, M. Botta, S. G. Crich, G. B. Giovenzana, G. Jommi, R. Pagliarin and M. Sisti, J. Chem. Soc., Chem. Commun., 1995, 1885; M. Inoue, R. E. Navarro, M. Inoue and Q. Fernando, Inorg. Chem., 1995, 34, 6074; D. E. Reichert, R. D. Hancock and M. J. Welch, Inorg. Chem., 1996, 35, 7013; E. Tóth, S. Vauthey, D. Pubanz and A. E. Merbach, Inorg. Chem., 1996, 35, 3375; D. H. Powell, O. M. Ni Dhubhghaill, D. Pubanz, L. Helm, Y. S. Lebedev, W. Schlaepfer and A. E. Merbach, J. Am. Chem. Soc., 1996, 118, 9333; G. R. Choppin and K. M. Schaab, Inorg. Chim. Acta, 1996, 252, 299.
3. C. Piguet, J.-C. G. Bünzli, G. Bernardinelli, G. Hopfgartner and A. F. Williams, J. Am. Chem. Soc., 1993, 115, 8197; C. Piguet, J.-C. G. Bünzli, G. Bernardinelli and A. F. Williams, Inorg. Chem., 1993, 32, 1237; C. Piguet, J.-C. G. Bünzli, G. Bernardinelli, C. G. Bochet and P. Froidevaux, J. Chem. Soc., Dalton Trans., 1995, 83; C. Piguet, G. Hopfgartner, A. F. Williams and J.-C. G. Bünzli, J. Chem. Soc., Chem. Commun., 1995, 491; C. Piguet, E. Rivara-Minten, G. Bernardinelli, J.-C. G. Bünzli and G. Hopfgartner, J. Chem. Soc., Dalton Trans., 1997, 421.
4. J.-M. Lehn, Supramolecular Chemistry, VCH, Weinheim, 1995, pp. 92–95 and refs. Therein; P. R. Selvin, J. Jancarik, M. Li and L.-W. Hung, Inorg. Chem., 1996, 35, 700; A. Døssing, H. Toftlund, A. Hazell, J. Bourassa and P. C. Ford, J. Chem. Soc., Dalton Trans., 1997, 335.
5. D. Parker and J. A. G. Williams, J. Chem. Soc., Dalton Trans., 1996, 3613.
6. W. D. Horrocks and D. R. Sudnick, Acc. Chem. Res., 1981, 14, 384; N. Sabbatini, M. Guardigli and J.-M. Lehn, Coord. Chem. Rev., 1993, 123, 201.
7. P. L. Jones, A. J. Amoroso, J. C. Jeffery, J. A. McCleverty, E. Psillakis, L. H. Rees and M. D. Ward, Inorg. Chem., 1997, 36, 10.
8. G. H. Frost, F. A. Hart and N. B. Hursthouse, Chem. Commun., 1969, 1421; D. A. Durham, G. H. Frost and F. A. Hart, J. Inorg. Nucl. Chem., 1969, 31, 833.
9. C. Piguet, J.-C. G. Bünzli, G. Bernardinelli and A. F. Williams, Inorg. Chem., 1993, 32, 4139.
10. C. Mallet, R. P. Thummel and C. Hery, Inorg. Chim. Acta, 1993, 210, 223.
11. C. Yang, X.-M. Chen, W.-H. Zhang, J. Chen, Y.-S. Yang and M.-L. Gong, J. Chem. Soc., Dalton Trans., 1996, 1767.
12. Y. Lin and S. A. Lang, J. Heterocycl. Chem., 1977, 14, 345.
13. T. Buchen, P. Gütlich, K. H. Sugiyarto and H. A. Goodwin, Chem. Eur. J., 1996, 2, 1134.
14. SHELXTL 5.03 program system, Siemens Analytical X-Ray Instruments, Madison, WI, 1995; Software package for use with the SMART diffractometer; Siemens Analytical X-Ray Instruments, Madison, WI, 1995.
15. S. Trofimenko, J. C. Calabrese and J. S. Thompson, Inorg. Chem., 1992, 31, 974 and refs. therein.
16. E. Psillakis, J. C. Jeffery, J. A. McCleverty and M. D. Ward, Chem. Commun., 1997, 479.
17. E. Psillakis, J. C. Jeffery, J. A. McCleverty and M. D. Ward, J. Chem. Soc., Dalton Trans., in the press.
18. A. Novak, Struct. Bonding (Berlin), 1974, 18, 177.
19. D. A. Bardwell, J. C. Jeffery, P. L. Jones, J. A. McCleverty and M. D. Ward, J. Chem. Soc., Dalton Trans., 1995, 2921.
20. S. Aime, M. Botta, D. Parker and J. A. G. Williams, J. Chem. Soc., Dalton Trans., 1996, 17.
21. R. D. Chapman, R. T. Loda, R. W. Riehl and R. W. Schwartz, Inorg. Chem., 1984, 23, 1652.
22. J.-C. G. Bünzli, J.-R. Yersin and C. Mabillaud, Inorg. Chem., 1982, 21, 1471; J.-C. G. Bünzli and A. Nilicic-Tang, Inorg. Chim. Acta, 1996, 252, 221.