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Observation of anomalous spin states of iron(II) in strong-field diimine complexes by57Fe mössbauer emission spectroscopy

1977; Elsevier BV; Volume: 45; Issue: 1 Linguagem: Inglês

10.1016/0009-2614(77)85201-9

1873-4448

J. Ensling, J H Fleisch, Philipp Gütlich, Β. W. Fitzsimmons,

Electron Spin Resonance Studies

Tris(2-pyridinalmethylimine)57 Co(II) perchlorate, [57Co(pmi)3] (CIO4)2 (pmi = 2-pyridinalmethylimine), and dicyanobis (1,10-phenanthroline)57 Co(II), [57Co(phen)2 (CN)2] · 2H2O, labelled with 270-day cobalt-57 have been prepared and employed as sources in Mössbauer emission spectroscopy measurements using an absorber of potassium hexacyanoferrate(II) enriched in iron-57. Spectra were measured at source temperatures between 293 and 4.2 K in case of [57Co(pmi)3] (CIO42) and between 264 and 78 K in case of [57Co(phen)2(CN)2 ·2h2O. The high-temperature spectra are predominantly quadrupole doublets arising from low-spin iron(II) in [FeN6]2+ environments, but at low temperatures additional resonances were observed and these have been assigned to short-lived high-spin iron(II) species. The electronic nature of these species is suggested to be consistent with 5A1(D3) and 5E(D3) for the two high-spin species in [57Co(pmi)3] (ClO4)2, respectively and 5A2(C2v) for the only high-spin species in case of [57Co(phen)2(CN)2] · 2H2O. The anomalous spin quintet states in the strong-filed environment have life times of the order of 100—400 ns at T≲ 80 K and are proposed to be the immediate precursors of the stable 1A1(Oh) product.