Heteroleptic iron(ii) complexes with naphthoquinone-type ligands

Abstract

Heteroleptic iron complexes with a naphthoquinone-type ligand, 2-(pyridin-2-yl)-1H-naphtho[2,3-d]imidazole-4,9-dione (HL), were synthesized, and their structures and magnetic properties were investigated. Two spin-crossover complexes, [Fe(L)₂(L¹)] (1, L¹ = ethylenediamine) and [Fe(L)₂(L²)] (2, L² = cyclohexanediamine) were structurally characterized at 100 K and 270 K, and their gradual spin crossover behavior observed by magnetic susceptibility measurements and confirmed by Mössbauer spectroscopic analyses. Two homologous iron(II) complexes, [Fe(L)₂(L^3c)] (3, L^3c = diimino benzoquinone) and [Fe(L)₂(L^4c)] (4, L^4c = iminosuccinonitrile), were found to exist in the low-spin state in the range of 10–300 K. In contrast, the corresponding complex with two water ligands, [Fe(L)₂(H₂O)₂] (5), and the tris-chelate complex with protonated ligands (HL), [Fe(HL)₃](BF₄)₂ (6), were found to be high-spin.