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Institutional Repository [SANDBOX]
Technical University of Crete
Technical University of Crete
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| URI: | http://purl.tuc.gr/dl/dias/8005805F-CC38-477C-B38E-07D1655AA467 | ||
| Year | 1999 | ||
| Type of Item | Peer-Reviewed Journal Publication | ||
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| Bibliographic Citation | K. V Mann, J. Jeffery, L. Rees, N. Harden, J. McCleverty, M. Ward, F. Mabbs, E. Psillakis, J. C Jeffery, L. H Rees, N. M Harden, J. A McCleverty, M.D Ward, D. Gatteschi, F. Totti, F. E Mabbs, E. JL McInnes, P. C Riedi, G. M Smithá, E. L McInnes, P. Riedi, G. Smith, "Tetranuclear grid-like copper(II) complexes with pyrazolate bridges: Syntheses, structures, magnetic and EPR spectroscopic properties ",J. Chem. Soc., Dalton Trans.,no.3 pp.339–348,1999.doi:10.1039/A807599I https://doi.org/10.1039/A807599I | ||
| Appears in Collections |
Reaction of 3-(2-pyridyl)pyrazole (HL1) and 6-(3-pyrazolyl)-2,29-bipyridine (HL2) with nickel(II) and zinc(II) saltsafforded the simple mononuclear pseudo-octahedral complexes [M(HL1)3][PF6]2 and [M(HL2)2][PF6]2 respectively(M = Ni or Zn) in which the ligands co-ordinate as neutral mononucleating chelates in the same manner as e.g.2,29-bipyridine or 2,29:69,20-terpyridine respectively. However with CuII the complexes [Cu4(L1)6(solv)2][PF6]2(solv = dmf or MeOH) and [Cu4(L2)4(dmf)4][PF6]4 were isolated and crystallographically characterised, in all casescontaining four tetragonally elongated square-pyramidal copper(II) ions which are linked by pyrazolate bridgesfrom the now deprotonated ligands L1 and L2. The approximate orthogonality of the different ligands within eachcomplex and the approximately square array of metal ions result in a grid-like structure. In [Cu4(L1)6(solv)2][PF6]2there are successively two, one, two and one pyrazolate bridges between adjacent copper(II) ions around the Cu4square resulting in two clearly different magnetic coupling pathways; in [Cu4(L2)4(dmf)4][PF6]4 however, whichhas approximate S4 symmetry, each Cu ? ? ? Cu edge has a single pyrazolate bridge and the coupling pathwaysare all virtually equivalent. Prolonged drying of these compounds resulted in loss of the axial dmf ligands togive [Cu4(L1)6][PF6]2 and [Cu4(L2)4][PF6]4. Magnetic susceptibility studies on these showed the presence of twoantiferromagnetic exchange pathways for [Cu4(L1)6][PF6]2 with J > 172 cm21 and J9 < 155 cm21 (strong correlationbetween the parameters precludes a more precise determination), but only one antiferromagnetic exchange pathwayfor [Cu4(L2)4][PF6]4 with J = 63.5 cm21, consistent with the crystal structures of the dmf adducts. The EPR spectraof [Cu4(L1)6][PF6]2 and [Cu4(L2)4][PF6]4 at a variety of frequencies and temperatures can be well simulated as arisingfrom triplet species; however the spectrum of [Cu4(L1)6][PF6]2 also contains a feature which may be ascribed to theexpected thermally populated quintet state.
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