Synthesis and Crystal Structure of Mononuclear Iron(III) Complex of 6-Hydroxy-2-(5-bromo-2-hydroxyphenyl)-5-(5-bromosalicylideneamino)-benzoxazole

Abstract

Self-assembly into polynuclear metal complexes can be achieved by the use of the multidentate ligands that possess the ability to bridge plural metal ions. 1-3 In our previous work, we reported on a trinuclear manganese (III) complex of 6-hydroxy-2-(2-hydroxyphenyl)-5-(salicylideneamino)benzoxazole (H3L), which was obtained by the reaction of a symmetrical ligand, 4,6-bis{(2-hydroxybenzylidene)imino}benzene-1,3-diol (H4L′), with manganese(II) acetate tetrahydrate. 4 The ligand H3L has an unsymmetrical structure comprised of ONO-tridentate and ON-bidentate coordination sites. It is expected that H3L can be utilized to obtain complex ligands, because two different coordination sites can bind to suitable metal ions. Here, we report on the crystal structure of the iron(III) complex, which has an unoccupied ON-coordination site.The precursor of H3L-Br (H4L′-Br·HCl) was synthesized from 4,6-diaminoresorcinol dihydrochloride (0.852 g, 4 mmol) and 5bromosalicylaldehyde (1.608 g, 8 mmol) in a similar manner as described in the literature. 4 H4L′-Br·HCl·2H2O (Yield: 1.41 g, 61%). C20H19Br2ClN2O6 (578.64): calcd. C 41.51, H 3.31, N 4.84; found C 41.27, H 3.23, N 4.91. To a solution of H4L′-Br·HCl (0.058 g, 0.1 mmol) in pyridine (10 cm 3 ) was added iron(III) chloride anhydrous (0.016 g, 0.1 mmol). The resulting light-brown solution was filtered. Dark-brown crystals were