Exploring the coordination chemistry of 3,3'-di(picolinamoyl)-2,2'-bipyridine: one ligand, multiple nuclearities

The syntheses, structures, and magnetic properties of three new coordination complexes, tetranuclear [Zn2L(3)(OAc)(OMe)]2·3MeOH·H2O (3), trinuclear [Ni3(L(3))3]·6H2O (4), and a 1-D chain {[Cu2L(3)(OAc)2]2·H2O}n (6), of a polydentate, doubly deprotonated, 3,3'-disubstituted bipyridine ligand [L(3)](2-) are reported. The X-ray crystal structures demonstrate that the ditopic ligand provides a flexible N3 donor set for transition metal ions where each binding pocket shifts from fac to intermediate fac/mer to the mer isomer affording a Ni3 triangle, a Zn4 tetramer, and a 1-D Cu(II) polymer, respectively. This variation in coordination preference is rationalized with the aim of designing future ligands with controlled coordination modes. Magnetic susceptibility studies on 4 reveal it belongs to the rare family of ferromagnetically coupled [Ni3] clusters. In contrast, magnetic studies of the 1-D chain 6 reveal weak antiferromagnetic interactions due to the poor orbital overlap of the singly occupied Cu(II) d(x(2)-y(2)) orbitals with the one-atom bridge that connects them along the Jahn-Teller distortion axis.