Reaction of divalent metal acetate and 2,2′-bipyridine. Syntheses and structural characterization of mono-, bi- and tri-nuclear complexes

The reactions of divalent metal acetate (M=CdII, CoII, CuII, MnII and NiII) with 2,2′-bipyridine (bpy) were systematically observed at a ratio of 1:1 in methanol solution. Three kinds of complexes were isolated: mononuclear [Ni(bpy)(OAc)2(H2O)2] (6), binuclear [Cd2(bpy)2(OAc)4(H2O)2] (7) and [Cu2(bpy)2(OAc)4]·2H2O (8), linear trinuclear [M3(bpy)2(OAc)6] (M=CoII (11) and MnII (12)). When 1.5 equivalent NaClO4 was added to the reaction solution, respectively two kinds of complexes were obtained: mononuclear [M(bpy)2(OAc)](ClO4)·nH2O (M=CdII (1), CoII (2), MnII (3) and NiII (4)) and binuclear [M2(bpy)2(μ-OAc)3](ClO4) (M=CuII (9) and ZnII (10)). The structures of complexes 1, 7 and 11 were determined by X-ray diffraction analysis. Complex 7 is the first example of a dicadmium complex linked by two monoatomic bridging acetate ligands with the longest distance of 3.380(4) Å between the dangling acetate oxygen and metal atoms. Several novel structural features in complex 7 have been found in comparison with the monodentate bridging carboxylate with no or only weak interaction between the dangling acetate oxygen atom and metal atom. The structure of complex 11 consists of linear trinuclear molecules; each pair of cobalt atoms are bridged by three acetate groups, two of them acting as bidentate bridging mode and the third as a monoatomic bridge plus bidentate chelating mode, at a distance of 3.459 Å. The central cobalt(II) coordinates by six oxygen atoms from six different acetate groups, and the terminal ones have a distorted environment of four oxygen atoms and two nitrogen atoms from a bpy ligand.