Two linear, trinuclear mixed‐valence complexes, [CoII{(μ‐L1)(μ‐OAc)CoIII(OAc)}2] (1) and [CoII{(μ‐L2)(μ‐OAc)CoIII(OAc)}2] (2) and two mononuclear CoIII complexes [CoIII{L3}(OAc)] (3), and [CoIII{L4}(OAc)] (4) were prepared and the molecular structures of 1, 2 and 4 elucidated on the basis of X‐ray crystallography [OAc = Acetate ion, H2L1 = H2Salen = 1,6‐bis(2‐hydroxyphenyl)‐2,5‐diazahexa‐1,5‐diene, H2L2 = H2Me2Salen = 2,7‐bis(2‐hydroxyphenyl)‐2,6‐diazaocta‐2,6‐diene, H2L3 = H2Salpn = 1,7‐bis(2‐hydroxyphenyl)‐2,6‐diazahepta‐1,6‐diene, H2L4 = H2Me2Salpn = 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 CoIIIN2O4 centres in 1 and 2 exhibit uniform facial arrangements of both non‐bridged N2O and bridging O3 donor sets and the CoII 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 CoII in both 1 and 2. The complexes 1 and 2 are thus CoIII(S = 0)–CoII(S = 3/2)–CoIII(S = 0) trimers. Complexes 3 and 4 are monomeric and diamagnetic containing low‐spin CoIII(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)
