Synthesis and crystal structures of Ni(II), Cu(II) and μ-oxo-Fe(III) complexes of a salen type ligand: Mononuclear versus multinuclear complex formation

The nickel, copper and iron complexes of bis(salicylidene)-meso-1,2-diphenylethylendiaminato (mdpSal2−) and their propensity to form multinuclear complexes similar to those observed for Co(mdpSal) are reported. The syntheses of the primary compounds were carried out with M(OAc)2·xH2O (M = Fe, Ni or Cu) and mdpSalH2 in methanol. The Ni and Cu reactions resulted in the isolation of mononuclear Ni(mdpSal) (1) and Cu(mdpSal) (2) complexes. Both species 1 and 2 adopt approximate square planar geometries in the monoclinic space group P21/n and are iso-structural to the previously reported Co(mdpSal). Although structurally similar, neither 1 nor 2 exhibit comparable reactivity as reported for the cobalt analogue of mdpSal−2 in forming multinuclear complexes. The iron reaction yielded a μ-oxo species [Fe(mdpSal)]2O (3) in which each iron center is oxidized to +3 and ligated to one mdpSal2− ligand frame with each iron center adopting distorted square pyramid geometry. In addition, Co(Salophen) (4) (SalophenH2 = N,N′-bis(salicylidene)-1,2-phenylenediamine) has been synthesized and its reactivity assessed and compared to Co(mdpSal). Complexes 1–3 have been characterized by X-ray crystallography as well as UV–Vis and IR spectroscopy. A detailed comparison of the structural and spectral characteristics of the iso-structural complexes 1 and 2 with Co(mdpSal) are presented along with a discussion of factors that contributed to the unique reactivity observed for [Co(mdpSal)].

Graphical abstractNickel, copper and μ-oxo-iron complexes of mdpSal2− are reported along with their propensity to form multinuclear complexes as observed for Co(mdpSal). For the monomeric species, similar reaction conditions (Path A: Addition of one drop of HCl. B: Slow evaporation of the mother liquor), resulted in only multinuclear complex formation for Co(mdpSal).Figure optionsDownload full-size imageDownload as PowerPoint slide