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A novel series of bis-complexes of iron(II) employing the bidentate ligand 2-methyl-1,10-phenanthroline

1972; Pergamon Press; Volume: 34; Issue: 9 Linguagem: Inglês

10.1016/0022-1902(72)80595-5

1878-1225

E. König, G. Ritter, K. Madeja, Asger Rosenkranz,

Electron Spin Resonance Studies

The synthesis and some physical properties of a series of bis(2-methyl-1,10-phenanthroline)-iron(II) complexes are reported. In nitromethane and acetonitrile, the compounds Fe(mephen)2X2 where X = Cl, Br, NCS, N3 and 12 mal (= malonate) are essentially non-electrolytes with a high-spin (5T2) ground state and exhibit, at 294°K, values of the magnetic moment μeff=5·09-5·42 BM. Between 77 and 300°K, the susceptibilities follow the Curie-Weiss law, χm = Cm/(T−Θ) with Θ = −2–−6°K. In the Mössbauer spectra at 294°K, isomer shifts δis = 1·00–1·08 mm sec−1 and quadrupole splittings ΔEQ = 1·84-2·58 mm sec−1 are obtained. The electronic spectra show, at ∼ 10,000 cm−1, the 5T2 → 5E transition within the d6 electron configuration, the excited 5E state being split by 2000–3000 cm−1. In Fe(mephen)2(NCS)2, the NCS groups are N-bonded and cis. The compound Fe(mephen)2(CN)2 has a low-spin (1A1) ground state and may be characterized by μeff = 1·02 BM, δis = 0·06 mm sec−1, and ΔEQ = 0·88 mm sec−1 at 294°K. In view of the recently studied spin equilibria in Fe(mephen)32+ complexes, it is concluded that, in the Fe(mephen)2X2 series, the crossover between the ground states 5T2 and 1A1 is exactly at the position of the mephen ligand in the spectrochemical series.