5T2 1A1 AND 6A1 2T2 SPIN TRANSITIONS IN IRON(II) AND IRON(III) COMPLEXES OF 2,2'-BI-2-IMIDAZOLINE AND RELATED LIGANDS

Article abstract of DOI:10.1039/DT9810001492

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 <(L-H = monodeprotonated ligand> 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.

Full text of DOI:10.1039/DT9810001492

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