Doubly pyridazine-bridged macrocyclic complexes of copper in + 1, + 2 and mixed valent oxidation states

Sally Brooker, Tony C. Davidson, Sarah J. Hay, Robert J. Kelly, Dietmar K. Kennepohl, Paul G. Plieger, Boujemaa Moubaraki, Keith S. Murray, Eckhard Bill, Eberhard Bothe

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65 Citations (Scopus)


Transmetallation of the dilead(II) complex [Pb2(L1′)](ClO4)4 [L1′ is the (4 + 4) Schiff-base macrocycle derived from 3,6-diformylpyridazine and 1,3-diaminopropane] with copper(II) perchlorate results in the formation of a dicopper(II) complex of the (2 + 2) Schiff-base macrocycle L1, Cu2II(L1)(ClO4)4 (1). Copper(II) is unable to template the formation of 1 from the organic precursors. A series of six dicopper(II) complexes of L1 has been prepared from 1, including: [Cu2II(L1)X2](ClO4)2 (where X = Cl- 2, Br- 3, I- 4, NCS- 5), Cu2II(L1)(H2O)2(NO3) 2(ClO4)2 (6) and Cu2II(L1)(H2O)2(ClO4) 4 (7). Three of these dicopper(II) complexes, 1·2MeCN, 2·H2O and 7, have been characterised by X-ray crystallography. In all three cases the (2 + 2) macrocycle provides a double pyridazine bridge between the two copper(II) ions. Magnetic studies show that the double pyridazine bridge mediates strong antiferromagnetic exchange between the copper(II) ions in all of these complexes ( - 2J = 412 to 532 cm-1). Electrochemical and spectroelectrochemical studies reveal that reduction of the dicopper(II) complexes occurs in two one electron steps, via stable mixed valent intermediates (Kc = 3.8 × 105 to 8.6 × 106 in acetonitrile, MeCN), in marked contrast to all previously studied pyridazine-bridged dicopper complexes. The thiocyanate salt of the mixed valent complex, [CuIICuI(L1)(NCS)4CuI]MeCN (9), has been isolated, by transmetallation of [Pb2(L1′)](ClO4)4 with copper(I) followed by the addition of NaNCS, and structurally characterised. Finally, the previously reported grid complex, [Cu4I(L1)2](PF6)4 (10) [formed by templating L1 formation on copper(I) ions], is shown by NMR spectroscopy to exist in equilibrium with another species, presumed to be a dicopper(I) complex, [Cu2I(L1)(MeCN)2](PF6) 2 (11), in acetonitrile solution. In support of this assignment, the structure of the dicopper(I) complex, [Cu2I(L1)(PPh3)2](PF 6)2 (12), isolated from reaction of 10 with two equivalents of PPh3, is reported.

Original languageEnglish
Pages (from-to)3-30
Number of pages28
JournalCoordination Chemistry Reviews
Publication statusPublished - 2001


  • Copper
  • Electrochemistry
  • Macrocycle
  • Mixed-valent
  • Pyridazine
  • X-ray crystal structure


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