Metal-Ion Tuning in Triple-Stranded Helicate-Based Metallosupramolecules

Effective incorporation of multiple types of ligands in a given coordination structure provides structural complexity and functional diversity to the resultant coordination-driven assembly. One of the most widely used synthetic approaches is the utilization of the molecular symmetry principle to combine multiple ligands and specific metallic centers in a preferred manner. The variation of metal ions can be helpful to understand the importance of symmetry for the generation of structurally hierarchical supramolecular platforms. We describe the synthesis and characterization of isostructural supramolecular helicates, [M₈ (PDA)₆ (AIP)₃ (DMF)_6-x (H₂ O)_x ] (M=Ni (1), Co (2), and Mn (3); PDA=2,6-pyridinedicarboxylate; AIP=5-aminoisophthalate; x=0 for 1, and x=4 for 2 and 3). The effect of metal variation on the formation of supramolecular helicates and their solid-state crystal packing are discussed. Despite the disparity in the ionic radii and distinct coordination-geometry preferences of Co²⁺ , Ni²⁺ , and Mn²⁺ , all metal centers engaged in the assembly with the heteroleptic ligands in the same manner to form isostructural supramolecular helicates.