Heteroleptic iron(ii) complexes with naphthoquinone-type ligands

摘要

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)(L-1)] (1, L-1 = ethylenediamine) and [Fe(L)(2)(L-2)] (2, L-2 = cyclohexanediamine) were structurally characterized at 100 K and 270 K, and their gradual spin crossover behavior observed by magnetic susceptibility measurements and confirmed by Mossbauer 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.