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

Fallis, Ian Andrew ORCID:, Farley, Richard D., Malik, K. M. Abdul, Murphy, Damien Martin ORCID: and Smith, Hayley J. 2000. Divalent first-row transition metal complexes of the rigid pendant-arm ligand 1,4,7-tris(2-aminophenyl)-1,4,7-triazacyclononane. Journal of the Chemical Society, Dalton Transactions 20 , pp. 3632-3639. 10.1039/b005402j

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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.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Publisher: Royal Society of Chemistry
ISSN: 1477-9226
Last Modified: 24 Oct 2022 11:32

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