Change in the Spin State of an FeIII Center upon One N-to-O Switch in the Coordination of a 2,6-Pyridinedicarboxamido Unit: The Effect of Methyl Thioether and Methyl Ether Appendages at the Ligand Periphery
✍ Scribed by Todd C. Harrop; Laurie A. Tyler; Marilyn M. Olmstead; Pradip K. Mascharak
- Publisher
- John Wiley and Sons
- Year
- 2003
- Tongue
- English
- Weight
- 136 KB
- Volume
- 2003
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
Abstract
Two ligands bearing the 2,6‐pyridinedicarboxamide unit, namely PyPSMeH~2~ and PyPOMeH~2~, have been used to prepare complexes of Fe^III^ which have been structurally characterised. The potentially pentadentate thioether ligand PyPSMeH~2~ affords only the bis complex (Et~4~N)[Fe(PyPSMe)~2~] (1), irrespective of the metal to ligand ratio, due to the weak affinity of the thioether groups for the Fe^III^ center. In [Fe(PyPSMe)~2~]^−^, the two PyPSMe^2−^ ligands bind to the iron center in a mer fashion and steric crowding among the pendant thioether groups forces one of the four deprotonated carboxamido moieties to bind to the Fe^III^ center through the carbonyl oxygen, giving rise to an FeN~5~O chromophore. The tridentate ligand PyPOMeH~2~, in its deprotonated form, also gives rise to a bis complex, (Et~4~N)[Fe(PyPOMe)~2~] (2), in which the two PyPOMe^2−^ ligands bind to the iron center in a mer fashion. In this case, however, less steric crowding among the smaller pendant ether groups allows binding of all four carboxamido nitrogens to the Fe^III^ center in [Fe(PyPOMe)~2~]^−^ giving rise to an FeN~6~ chromophore. This one N‐to‐O switch in donor atom makes the two complexes 1 and 2 very different. While complex 2 is low spin (g = 2.18, 1.94) much like the other reported Fe^III^ bis complexes with two ligated 2,6‐pyridinedicarboxamido units, complex 1 is high spin (g = 4.3). The spin flip due to a switch in only one N or O donor atom in these two complexes is unprecedented. The two complexes also exhibit different stability towards water. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)