Metal directed self-assembly of Tetranuclear $$\hbox {Cu}^{\mathrm{II}}$$CuII and $$\hbox {Ni}^{\mathrm{II}}$$NiII clusters

The self-assembly of two pyridine hydrazone based tritopic ligands appended with terminal carboxylate groups with \(\hbox {Cu}^{\mathrm{II}}\) and \(\hbox {Ni}^{\mathrm{II}}\) have been investigated. These polytopic ligands with tridentate coordination pockets were designed to produce homoleptic [\(3\times 3\)] grid complexes on reaction with transition metals. Despite the formation of anticipated metallogrids as the final self-assembly outcome, metal ion geometric preferences and ligand flexibility lead to the formation of tetranuclear clusters in the self-assembly process with \(\hbox {Cu}^{\mathrm{II}}\) and \(\hbox {Ni}^{\mathrm{II}}\) metal ions. These results illustrate the dynamic nature of the metal–ligand interactions and flexible nature of the ligand backbone in coordination self-assembly. The synthesis, structure and magnetic properties of three tetraanuclear species {[\(\hbox {Cu}_{4}(\hbox {H}_{2}\hbox {L}^{\mathrm{1b}})_{2}(\hbox {OTf})_{4}(\hbox {OH})_{2}(\hbox {H}_{2}\hbox {O})_{2}\)]\(\cdot 6\hbox {H}_{2}\hbox {O}\}_{\mathrm{n}}\) (1), [\(\hbox {Ni}_{4}(\hbox {L}^{\mathrm{2a}})_{2}(\hbox {OCH}_{3})_{4}]{\cdot }4\hbox {H}_{2}\hbox {O}\) (2), [\(\hbox {Cu}_{4}(\hbox {L}^{\mathrm{2b}})_{2}(\hbox {OTf})_{4}(\hbox {H}_{2}\hbox {O})_{4}]{\cdot }6\hbox {H}_{2}\hbox {O}\) (3) involving two tritopic ligands with central pyridine framework are described.