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 [Zn2L3(OAc)­(OMe)]2·3MeOH·H2O (3), trinuclear [Ni3(L3)3]·6H2O (4), and a
1-D chain {[Cu2L3(OAc)2]2·H2O}n (6), of a polydentate, doubly deprotonated, 3,3′-disubstituted
bipyridine ligand [L3]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) dx2–y2 orbitals with the one-atom bridge that connects them along the Jahn–Teller
distortion axis.