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Issue 20, 2000
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Divalent first-row transition metal complexes of the rigid pendant-arm ligand1,4,7-tris(2-aminophenyl)-1,4,7-triazacyclononane

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Abstract

The rigid pendant-arm macrocyclic ligand 1,4,7-tris(2-aminophenyl)-1,4,7-triazacyclononane (L1) has been synthesized. It reacts with divalent first row transition metal perchlorate salts to yield complexes of general formula [MII(L1)][ClO4]2 (M = FeII, NiII, CuII or ZnII). Single crystal X-ray crystallography indicated that [FeII(L1)][ClO4]2 and [NiII(L1)][ClO4]2 are isostructural with both complex cations consisting of distorted pseudo-octahedral six-co-ordinate metal centres with three macrocyclic N-donors and three anilino donors. The mean Fe–N bond length in [FeII(L1)][ClO4]2 was found to be 2.10 Å, which is intermediate between the normal ranges of high and low spin FeIIN6 species. Magnetometry and EPR measurements indicated that single crystals of [FeII(L1)][ClO4]2 were predominately low spin, with approximately 5% of a low spin iron(III) species present in the lattice. It is postulated that this latter species is the mono anilido complex [FeIII(L1  H)][ClO4]2. The crystal structure of [NiII(L1)][ClO4]2 indicated a short mean Ni–N bond length of 2.09 Å. The ligand field strength for this material was found to have a very high value of 12,330 cm−1 (B = 850 cm−1) and is compared to that of some related trigonal NiIIN6 species. The crystal structure of [CuII(L1)][ClO4]2 was also determined and indicated a distorted six-co-ordinate metal centre. The X-band EPR spectrum of this complex in magnetically dilute solid solution indicated a predominantly axial species, although a slight rhombic distortion may be present. The variable temperature 1H NMR of [ZnII(L1)][ClO4]2 in CD3CN solution revealed a non-fluxional six-co-ordinate complex. Electrochemical analyses of the complexes indicated only irreversible oxidation and reduction processes for [NiII(L1)][ClO4]2 and [CuII(L1)][ClO4]2. [FeII(L1)][ClO4]2 displays at least two reversible oxidation processes with the first at +0.181 V (vs. Fc–Fc+) being assigned as a metal centred FeII → FeIII process and the second at +0.475 V as a ligand centred process.

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Supplementary files

Article information


Submitted
05 Jul 2000
Accepted
06 Sep 2000
First published
03 Oct 2000

J. Chem. Soc., Dalton Trans., 2000, 3632-3639
Article type
Paper

Divalent first-row transition metal complexes of the rigid pendant-arm ligand 1,4,7-tris(2-aminophenyl)-1,4,7-triazacyclononane

I. A. Fallis, R. D. Farley, K. M. A. Malik, D. M. Murphy and H. J. Smith, J. Chem. Soc., Dalton Trans., 2000, 3632 DOI: 10.1039/B005402J

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