Metal directed self-assembly of Tetranuclear Cu^II and Ni^II clusters

The self-assembly of two pyridine hydrazone based tritopic ligands appended with terminal carboxylate groups with Cu^II and Ni^II have been investigated. These polytopic ligands with tridentate coordination pockets were designed to produce homoleptic [ 3× 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 Cu^II and Ni^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 [ Cu_4(H_2L^1b)_2(OTf)_4(OH)_2(H_2O)_2 ] · 6H_2O}_n ( 1 ), [ Ni_4(L^2a)_2(OCH_3)_4]·4H_2O ( 2 ), [ Cu_4(L^2b)_2(OTf)_4(H_2O)_4]·6H_2O ( 3 ) involving two tritopic ligands with central pyridine framework are described. GRAPHICAL ABSTRACT Synopsis: Metal Directed Self-Assembly of Tetra Nuclear Cu^II and Ni^II Clusters Avinash Lakma, Sayed Muktar Hossain, Rabindranath Pradhan and Akhilesh Kumar Singh ...................xxxx-xxxx Three tetranuclear non-grid complexes have been synthesized by reacting two pyridine hydrazone-based tritopic ligands with Cu^II and Ni^II salts. All complexes are spectroscopically and structurally characterized and their magnetic properties have been studied.