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Issue 4, 1999
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Copper(II) complexes of new potentially hexadentate N3S3- or N6-donor podand ligands based on the tris(pyrazolyl)borate or tris(pyrazolyl)methane core

Abstract

The mononuclear copper(II) complexes of the following potentially hexadentate podand ligands have been prepared and crystallographically characterised: tris[3-{2-(methylsulfanyl)phenyl}pyrazol-1-yl]hydroborate [L1]-, phenyltris[3-(2-pyridyl)pyrazol-1-yl]methane (L2), and tris[3-{(6-methyl)-pyrid-2-yl}pyrazol-1-yl]hydroborate [L3]-. Of these, [L1]- [a potentially N3S3 donor with three pyrazolyl and three thioether groups, based on a tris(pyrazolyl)borate core] and L2 [a potentially N6 donor with three pyrazolyl and three pyridyl groups, based on a tris(pyrazolyl)methane core] have been prepared for the first time. In [Cu(L1)][PF6] the Cu(II) centre is in a five-coordinate N3S2 coordination environment which is approximately square pyramidal; the pendant thioether group has a weak, long-range interaction with the sixth coordination site of Cu(II). [Cu(L1)][PF6] undergoes a reversible Cu(I)–Cu(II) redox conversion. In [Cu(L2)(MeOH)][PF6]2 the ligand is four-coordinate via two bidentate pyridyl/pyrazolyl arms, with the third arm pendant; an axial methanol ligand completes the square-pyramidal coordination. In [Cu(L3)(H2O)][PF6], which is five coordinate and approximately trigonal bipyramidal, [L3]- acts as an N4 donor via all three pyrazolyl groups but only one pyridyl group; the two pendant pyridyl groups are involved in O–H···N hydrogen-bonding interactions with the coordinated water molecule. This ‘second-sphere’ stabilisation of a coordinated ligand is strongly reminiscent of the cooperative interactions by which substrates are bound to the active sites of metalloproteins. The EPR spectra of this complex are solvent-dependent, showing a change from a dz2 ground state in non-donor solvents to a dx2-y2 ground state in donor solvents.

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Supplementary files


Article type: Paper
DOI: 10.1039/A809777A
Citation: New J. Chem., 1999,23, 417-424

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    Copper(II) complexes of new potentially hexadentate N3S3- or N6-donor podand ligands based on the tris(pyrazolyl)borate or tris(pyrazolyl)methane core

    E. R. Humphrey, K. L. V. Mann, Z. R. Reeves, A. Behrendt, J. C. Jeffery, J. P. Maher, J. A. McCleverty and M. D. Ward, New J. Chem., 1999, 23, 417
    DOI: 10.1039/A809777A

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