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 [Zn₂<b>L</b>^<b>3</b>(OAc)­(OMe)]₂·3MeOH·H₂O (<b>3</b>), trinuclear [Ni₃(<b>L</b>^<b>3</b>)₃]·6H₂O (<b>4</b>), and a 1-D chain {[Cu₂<b>L</b>^<b>3</b>(OAc)₂]₂·H₂O}_n (<b>6</b>), of a polydentate, doubly deprotonated, 3,3′-disubstituted bipyridine ligand [<b>L</b>^<b>3</b><b>]</b>^<b>2‑</b> 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 <i>fac</i> to intermediate <i>fac</i>/<i>mer</i> to the <i>mer</i> 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 <b>4</b> reveal it belongs to the rare family of ferromagnetically coupled [Ni₃] clusters. In contrast, magnetic studies of the 1-D chain <b>6</b> reveal weak antiferromagnetic interactions due to the poor orbital overlap of the singly occupied Cu­(II) d_{<i>x</i>²–<i>y</i>²} orbitals with the one-atom bridge that connects them along the Jahn–Teller distortion axis