Methylene Spacer‐Regulated Structural Variation in Cobalt(II/III) Complexes with Bridging Acetate and Salen‐ or Salpn‐Type Schiff‐Base Ligands

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)