Synthesis, magnetism, ¹H NMR and redox activity of dicopper(II) complexes having a discrete {Cu₂(µ-phenoxide)₂}²⁺ unit supported by a non-macrocyclic ligand environment. Crystal structure of [Cu₂(L)₂(OClO₃)₂] [HL = 4-methyl-2,6-bis(pyrazol-1-ylmethyl)phenol] †

Abstract

Reaction between 4-methyl-2,6-bis(pyrazol-1-ylmethyl)phenol (HL) or its 3,5-dimethylpyrazole derivative (HL′ ) and Cu(ClO₄)₂·6H₂O afforded [Cu^II₂(L/L′ )₂(OClO₃)₂] 1 and 2. Complex 1 has been structurally characterized showing that each copper(II) centre is square pyramidal with two bridging phenoxide oxygens and two terminal pyrazole nitrogens in the equatorial plane and a perchlorate oxygen atom axially co-ordinated. Variable-temperature magnetic susceptibility measurements revealed that the dicopper(II) centres are strongly antiferromagnetically coupled [singlet–triplet energy separation, 2J (in cm^–1): –1204 for 1 and –798 for 2]. The complexes exhibit ¹H NMR spectra within δ 0–10 due to their S = 0 ground state. In MeCN solution they exhibit ligand field transitions in the range 14 300–16 600 cm^–1 and phenolate-to-copper(II) charge-transfer transition at ≈ 22 700 cm^–1. In MeCN solution each complex displays three consecutive irreversible responses (scan rate of 50 mV s^–1) with E_pc values (V vs. SCE) at –0.02, –0.54 and –0.86 (1) and 0.00, –0.42 and –0.80 (2). The first two responses are due to Cu^II–Cu^I and the most cathodic response to Cu^I–Cu⁰ redox processes, respectively.

References

1. J. D. Crane, D. E. Fenton, J.-M. Latour and A. J. Smith, J. Chem. Soc., Dalton Trans., 1991, 2979; S. Uozumi, M. Ohba, H. Okawa and D. E. Fenton, Chem. Lett., 1997, 673.
2. (a) Y. Nishida, T. Tokii and Y. Mori, J. Chem. Soc., Chem. Commun., 1988, 675; (b) K. J. Oberhausen, J. F. Richardson, R. M. Buchanan, J. K. McCusker, D. N. Hendrickson and J.-M. Latour, Inorg. Chem., 1991, 30, 1357; (c) M. Lubben, R. Hage, A. Meetsma, K. Byma and B. L. Ferringa, Inorg. Chem., 1995, 34, 2217; (d) J. Reim and B. Krebs, J. Chem. Soc., Dalton Trans., 1997, 3793; (e) P. Amudha, M. Kandaswamy, L. Govindasamy and D. Velmurugan, Inorg. Chem., 1998, 37, 4486.
3. S. K. Dutta, K. K. Nanda, U. Flörke, M. Bhadbhade and K. Nag, J. Chem. Soc., Dalton Trans., 1996, 2371 2371 and refs. therein.
4. (a) N. Kitajima and Y. Moro-oka, Chem. Rev., 1994, 94, 737; (b) E. I. Solomon, U. M. Sundaram and T. E. Machonkin, Chem. Rev., 1996, 96, 2563; (c) K. D. Karlin, S. Kaderli and A. D. Zuberbühler, Acc. Chem. Res., 1997, 30, 139; (d) W. B. Tolman, Acc. Chem. Res., 1997, 30, 227.
5. F. Zippel, F. Ahlers, R. Werner, W. Haase, H.-F. Noltine and B. Krebs, Inorg. Chem., 1996, 35, 3409.
6. (a) D. Ghosh, T. K. Lal, S. Ghosh and R. Mukherjee, Chem. Commun., 1996, 13; (b) D. Ghosh and R. Mukherjee, Inorg. Chem., 1998, 37, 6597.
7. N. Kitajima, T. Koda, Y. Iwata and Y. Moro-oka, J. Am. Chem. Soc., 1990, 112, 8833.
8. (a) H. Adams, N. A. Bailey, D. E. Fenton, Q. He, M. Ohba and H. Okawa, Inorg., Chim. Acta, 1994, 215, 1; (b) H. Adams, N. A. Bailey, I. K. Campbell, D. E. Fenton and Q.-Y. He, J. Chem. Soc., Dalton Trans., 1996, 2233.
9. (a) J. C. Jeffery, J. P. Maher, C. A. Otter, P. Thornton and M. D. Ward, J. Chem. Soc., Dalton Trans., 1995, 819; (b) D. Black, A. J. Blake, K. P. Dancey, A. Harrison, M. McPartlin, S. Parsons, P. A. Tasker, G. Whittaker and M. Schröder, J. Chem. Soc., Dalton Trans., 1998, 3953.
10. (a) M. M. Whittaker, W. R. Duncan and J. W. Whittaker, Inorg. Chem., 1996, 35, 382; (b) S. Itoh, S. Takayama, R. Arakawa, A. Furuta, M. Komatsu, A. Ishida, S. Takamuku and S. Fukuzumi, Inorg. Chem., 1997, 36, 1407; (c) Y. Sunatsuki, M. Nakamura, N. Matsumoto and F. Kai, Bull. Chem. Soc. Jpn., 1997, 70, 1851; (d) M. Vaidyanathan, R. Viswanathan, M. Palaniandavar, T. Balasubramanian, P. Prabhakaran and T. P. Muthiah, Inorg. Chem., 1998, 37, 6418.
11. K. D. Karlin, B. I. Cohen, R. R. Jacobson and J. Zubieta, J. Am. Chem. Soc., 1987, 109, 6194.
12. (a) M. Ray, S. Mukerjee and R. Mukherjee, J. Chem. Soc., Dalton Trans., 1990, 3635; (b) M. Ray, D. Ghosh, Z. Shirin and R. Mukherjee, Inorg. Chem., 1997, 36, 3568; (c) A. K. Patra and R. Mukherjee, Polyhedron, 1999, 18, 1317.
13. C.-T. Chen, W.-K. Chang, S.-C. Sheu, G.-H. Lee, T.-I. Ho, Y.-C. Lin and Y. Wang, J. Chem. Soc., Dalton Trans., 1991, 1569.
14. T. N. Sorrell, C. J. O'Connor, O. P. Anderson and J. H. Reibenspies, J. Am. Chem. Soc., 1985, 107, 4199.
15. R. S. Drago, M. J. Desmond, B. B. Corden and K. A. Miller, J. Am. Chem. Soc., 1983, 105, 2287.
16. C. J. O'Connor, Prog. Inorg. Chem., 1982, 29, 203.
17. S. R. Hall, H. D. Flack and J. M. Stewart(Editors), The XTAL 3.2 Reference Manual, Universities of Western Australia, Geneva and Maryland, 1992.
18. S. F. Pavkovic and D. W. Meek, Inorg. Chem., 1965, 4, 1091; M. R. Rosenthal, J. Chem. Educ., 1973, 50, 331.
19. W. J. Geary, Coord. Chem. Rev., 1971, 7, 81.
20. A. W. Addison, T. N. Rao, J. Reedijk, J. van Rijn and G. C. Verschoor, J. Chem. Soc., Dalton Trans., 1984, 1349.
21. R. Mukherjee, Coord. Chem. Rev., in the press.
22. (a) G. Alzuet, L. Casella, M. L. Villa, O. Carugo and M. Gullotti, J. Chem. Soc., Dalton Trans., 1997, 4789; (b) F. Calderazzo, F. Marchetti, G. Dell'Amico, G. Pelizzi and A. Colligiani, J. Chem. Soc., Dalton Trans., 1980, 1419.
23. (a) S. K. Dutta, U. Flörke, S. Mohanta and K. Nag, Inorg. Chem., 1998, 37, 5029; (b) L. K. Thompson, S. K. Mandal, S. S. Tandon, J. N. Bridson and M. K. Park, Inorg. Chem., 1996, 35, 3117 3117 and refs. therein.
24. P. J. Hay, J. C. Thibeault and R. Hoffmann, J. Am. Chem. Soc., 1975, 97, 4885; C. J. Gal, J. Jaud, O. Kahn and P. Tola, Inorg. Chim. Acta, 1979, 36, 229; O. Kahn, Inorg. Chim. Acta, 1982, 62, 3; M. Melník, Coord. Chem. Rev., 1982, 42, 259.
25. B. J. Hathaway, in Comprehensive Coordination Chemistry, eds. G. Wilkinson, R. D. Gillard and J. A. McCleverty, Pergamon, Oxford, 1987, vol. 5, p. 533.
26. I. Bertini and C. Luchinat, NMR of Paramagnetic Molecules in Biological Systems, Benjamin-Cummings, Boston, 1986.
27. J. H. Satcher, jun. and A. L. Balch, Inorg. Chem., 1995, 34, 3371.