Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 131, Issue 35, Pages 12693-12702Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja903439t
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Funding
- National Science Foundation [CHE-0641020]
- National Institutes of Health [GM 48249]
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The monomeric iron(II) amido derivatives Fe{N(H)Ar*}(2) (1), Ar* = C6H3-2,6-(C6H2-2,4,6-Pr-3(i))(2), and Fe{N(H)Ar-#}(2) (2), Ar-# = C6H3-2,6-(C6H2-2,4,6-Me-3)(2), were synthesized and studied in order to determine the effects of geometric changes on their unusual magnetic properties. The compounds, which are the first stable homoleptic primary amides of iron(II), were obtained by the transamination of Fe{N(SiMe3)(2)}(2), with HN(SiMe3)(2) elimination, by the primary amines H2NAr* or H2NAr#. X-ray crystallography showed that they have either strictly linear (1) or bent (2, N-Fe-N = 140.9(2)degrees) iron coordination. Variable temperature magnetization and applied magnetic field Mossbauer spectroscopy studies revealed a very large dependence of the magnetic properties on the metal coordination geometry. At ambient temperature, the linear 1 displayed an effective magnetic moment in the range 7.0-7.50 mu(B), consistent with essentially free ion magnetism. There is a very high internal orbital field component, H-L approximate to 170 T which is only exceeded by a H-L approximate to 203 T of Fe{C(SiMe3)(3)}(2). In contrast, the strongly bent 2 displayed a significantly lower mu(eff) value in the range 5.25-5.80 mu(B) at ambient temperature and a much lower orbital field H-L value of 116 T. The data for the two amido complexes demonstrate a very large quenching of the orbital magnetic moment upon bending the linear geometry. In addition, a strong correlation of H-L with overall formal symmetry is confirmed. ESR spectroscopy supports the existence of large orbital magnetic moments in 1 and 2, and DFT calculations provide good agreement with the physical data.
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