SPECTROSCOPIC AND MAGNETIC-PROPERTIES AND STRUCTURE OF A 5-COORDINATE, O-2-BINDING COBALT(II) SCHIFF-BASE COMPLEX AND OF THE COPPER(II) ANALOG

The cobalt(II) complex CoL and the copper(II) complex CuL of the penta dentate O2N2N' Salen-type Schiff base ligand H2L = ethylbenzyliden)-1, 7-diamino-4-methyl-4-azaheptane were prepared, characterized and subje cted to single crystal X-ray analysis. The {MO2N2N'} coordination core forms a trigonal bipyramid differing in the degree of distortion, as expressed by the O-M-O angles 138.62(8)degrees [O-Co-O] and 155.21(7)d egrees [O-Cu-O]. The distances between the metal and the aliphatic ter tiary nitrogen atoms N' are markedly different, 2.123(2) [Co-N'] and 2 .300(2) Angstrom [Cu-N']. In contrast to normal Salen complexes the im ine nitrogen atoms are located trans to each other. Solution room temp erature electron spectra show a broad absorption in the near-IR range at 6350 (CoL) and 8200 (CuL) cm(-1). The temperature dependence of the effective magnetic moment for high-spin CoL (S = 3/2) shows a maximum at 50 K, which is reproduced by the following set of magnetic paramet ers, reflecting the zero-field splitting: g(x) = 1.68, g(y) = 1.89, g( z) = 3.21, D/hc = -38.9 cm(-1), E/hc = 1.7 cm(-1), alpha(TIP) = 0, zJ/ hc = -1.00 cm(-1). Variable temperature electron paramagnetic resonanc e experiments prove that CoL, dissolved in toluene, N,N-dimethylformam ide or pyridine, binds dioxygen reversibly. (C) 1998 Elsevier Science S.A. All rights reserved.