Methylene Spacer-Regulated Structural Variation in Cobalt(II/III) Complexes with Bridging Acetate and Salen- or Salpn-Type Schiff-Base Ligands
✍ Scribed by Shouvik Chattopadhyay; Michael G. B. Drew; Ashutosh Ghosh
- Publisher
- John Wiley and Sons
- Year
- 2008
- Tongue
- English
- Weight
- 256 KB
- Volume
- 2008
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
Abstract
Two linear, trinuclear mixed‐valence complexes, [Co^II^{(μ‐L^1^)(μ‐OAc)Co^III^(OAc)}~2~] (1) and [Co^II^{(μ‐L^2^)(μ‐OAc)Co^III^(OAc)}~2~] (2) and two mononuclear Co^III^ complexes [Co^III^{L^3^}(OAc)] (3), and [Co^III^{L^4^}(OAc)] (4) were prepared and the molecular structures of 1, 2 and 4 elucidated on the basis of X‐ray crystallography [OAc = Acetate ion, H~2~L^1^ = H~2~Salen = 1,6‐bis(2‐hydroxyphenyl)‐2,5‐diazahexa‐1,5‐diene, H~2~L^2^ = H~2~Me~2~Salen = 2,7‐bis(2‐hydroxyphenyl)‐2,6‐diazaocta‐2,6‐diene, H~2~L^3^ = H~2~Salpn = 1,7‐bis(2‐hydroxyphenyl)‐2,6‐diazahepta‐1,6‐diene, H~2~L^4^ = H~2~Me~2~Salpn = 2,8‐bis(2‐hydroxyphenyl)‐3,7‐diazanona‐2,7‐diene]. In complexes 1 and 2, the acetate groups show both monodentate and bridging bidentate coordination modes, whereas chelating bidentate acetate is present in 4. The terminal Co^III^N~2~O~4~ centres in 1 and 2 exhibit uniform facial arrangements of both non‐bridged N~2~O and bridging O~3~ donor sets and the Co^II^ centre is coordinated to six (four phenoxo and two acetato) oxygen atoms of the bridging ligands. The effective magnetic moment at room temperature corresponds to the presence of high‐spin Co^II^ in both 1 and 2. The complexes 1 and 2 are thus Co^III^(S = 0)–Co^II^(S = 3/2)–Co^III^(S = 0) trimers. Complexes 3 and 4 are monomeric and diamagnetic containing low‐spin Co^III^(S = 0) with chelating tetradentate Schiff base and bidentate acetate. Calculations based on DFT rationalise the formation of trinuclear or mononuclear complexes.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)