- 5T2 1A1 AND 6A1 2T2 SPIN TRANSITIONS IN IRON(II) AND IRON(III) COMPLEXES OF 2,2'-BI-2-IMIDAZOLINE AND RELATED LIGANDS
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A series of six-co-ordinate iron(II) complexes IIL3>X2 (X =ClO4 or BPh4) of the bidentate ligands 2,2'-bi-2-imidazoline (L3), 2,2'-bi-1,4,5,6-tetrahyropyrimidine (L4), 2,2'-bi-2-oxazoline (L5), and 5,5'-dimethyl-2,2'-bi-2-oxazoline (L6) have been prepared and characterised by their physical properties.In all cases co-ordination is via the α-di-imine group.Magnetic susceptibility and Moessbauer effect measurements as a function of temperature show that the complexes of L5 and L6 are fully high-spin (S = 2) over the temperature range 90-360 K, while for complexes of L3 (X = ClO4 but not BPh4) and L4 (X = ClO4 and BPh4) a 5T2 1A1 spin transition is observed in this temperature range.Electronic spectra of the corresponding nickel(II) complexes indicate a correlation between Dq(Ni) and the spin ground state of the iron(II) complexes.The iron(III) complex IIIL33>3 is high-spin (S=5/2), while 43>3 has a 2T2 ground state but with a thermally accessible 6A1 excited state.Iron(III) complexes of L5 and L6 are unstable and could not be isolated.Reaction of the iron(II) complexes of L3 and L4 with dioxygen gave the iron(III) complexes IIIL2(L-H)>2 in good yield which may be reversibly converted to the IIIL3>(3+) species on treatment with one equvivalent og HClO4.The temperature-dependent magnetic moments of the complexes 2(L-H)>2 are interpreted in terms of 2T2 6A1 spin equlibria.
- Burnett, Michael G.,McKee, Vickie,Nelson, S. Martin
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p. 1492 - 1497
(2007/10/02)
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