The template reaction of salicylaldehyde and its substituted derivatives and 2-hydroxy-5-bromobenzylamine or 2-hydroxy-5-chlorobenzylamine with copper(II) acetate in dimethyl sulphoxide (dmso) afforded eight dinuclear Cu(II) complexes, [Cu2(L)2(dmso)2] (H2 L = N-salicylidene-2-hydroxy-5-bromobenzylamine, N-salicylidene-2-hydroxy-5-chlorobenzylamine and their 5-bromo, 5-nitro and 5-methyl-substituted salicylidene derivatives). These Cu(II) complexes were characterised by IR and UV-VIS-NIR spectroscopy, electric conductivity, cyclic voltammetry, and temperature dependence of magnetic susceptibilities (4.5–300 K). In the THF solution, the complexes are nonelectrolytes and exhibit a characteristic CT band due to phenoxido-bridging at 360–384 nm. In the cyclic voltammograms, an irreversible reduction process was observed at −1.18–1.54 V vs Fc/Fc+. Single-crystal X-ray crystallography revealed that two Cu(II) ions were bridged by the two phenoxido-oxygen atoms of the two Schiff-base ligands with axial coordination of dmso molecules forming a square pyramid with a Cu-Cu distance of 3.0628(8)–3.0931(6) °A. In accordance with the crystal structures, the magnetic interaction between the two Cu(II) ions is relatively anti-ferromagnetic with −2J value of 386–575 cm−1. The axial coordination effect of the dmso molecule was discussed in relation to the correlation between the Cu-O-Cu angle and the −2J value.
N-Salicylidene-2-hydroxybenzylamine and its substituted derivatives are unique ligands having two phenolic-oxygen and one imino-nitrogen donor atoms, forming mononuclear manganese(IV) 1 and vanadium(IV) 2 complexes and dinuclear vanadium(V), 2 iron(III), 3 and copper(II) 4 complexes with a meridional O,N,O-chelating. Recently, we found that one of these ligands forms a hydrogen-bonded dimer structure in the crystal. 5 Concerning the dimer structure, we are interested in the dinuclear structure of phenoxo-bridged copper(II) complexes with these ligands. Although we reported on the crystal structure for one of these, the title compound, before (Fig. 1), the X-ray diffraction data were measured at room temperature and were not sufficient to get good-quality data, and the structural detail had not been described in the literature. 4 We also reported preliminary magnetic susceptibility data, and interpreted the magnetic data by a dimer model based on the room-temperature structure. 4 In order to understand the magnetic property of the complex exactly, it is desirable to confirm the low-temperature structure. In this study, we determined the crystal structure of the title compound at 90 K.The title compound was prepared by a previously reported procedure. 4 A mixture of 2-hydroxy-5-bromobenzylamine (20 mg, 0.1 mmol) and salicylaldehyde (12 mg, 0.1 mmol) dissolved in 3 mL of dimethyl sulfoxide was heated gently. To this solution was added copper(II) acetate (18 mg, 0.1 mmol), and the mixture was heated with stirring for 40 min, and then filtered. The resulting green solution was allowed to stand at X-ray Structure Analysis Online
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