Homo- and hetero-dinuclear metal complexes of bridging ligands containing phenol and azole moieties. Structure, spectroscopy, electrochemistry and magnetochemistry

Abstract

A series of phenoxo-bridged homo- and hetero-dinuclear complexes of 4-methyl-2,6-bis(5-methylpyrazol-3-yl)-phenol (H₃L¹) have been synthesized and characterized. Variable-temperature magnetic susceptibility measurements carried out for the homo-dinuclear complexes [Cu₂(H₂L¹)₂][ClO₄]₂1, [Cu₂(H₂L¹)(acac)₂][ClO₄]2, [Cu₂(H₂L¹)(µ-OH)Cl₂]3, [Ni₂(H₂L¹)₂(H₂O)₄][ClO₄]₂4 and [Fe₂(H₂L¹)₄(µ-OH)₂]·4H₂O 7 have shown that in all the cases the dinuclear metal centres are antiferromagnetically coupled with the following values of the exchange coupling constant J: –242 (1), –55 (2), –170 (3), –24 (4) and –11 cm^–1(7). The ESR spectra of the heterodinuclear complexes [ZnCu(H₂L¹)₂][ClO₄]₂·2H₂O 5 and [ZnMn(H₂L¹)₂Cl₂]6 have been examined. The ¹H NMR spectra of the dicopper(II) complexes 1 and 2 are reasonably sharp and the isotropic shifts of 1 are relatively less compared to those of 2. The crystal structures of 7 and 2·CHCl₃ have been determined. That of 7 comprises two edge-shared sterically non-equivalent FeO₄N₂ distorted octahedra. The structure of 2·CHCl₃ consists of two nearly square-planar copper(II) centres supported by a phenoxide bridge. The cryomagnetic behaviour of two phenoxo-bridged dimeric iron(III) complexes derived from a bis(iminomethyl)triphenol and a bis(aminomethyl)triphenol have also been studied.