Controllable Syntheses of a Two-Dimensional Coordination Framework and Its Discrete Heteroleptic Building Blocks

Controllable syntheses of a two-dimensional (2D) coordination polymer and its discrete triple-stranded helicate (TSH) building units using a solvent-assisted approach are reported. In a single TSH, two multinuclear nickel clusters, each assembled from four nickel ions and three 2,6-pyridinedicarboxylates, are interconnected by three V-shaped 4,4′-pyridine-2,6-diyldibenzoate (PDDB) bridging ligands. The long distance between two terminal carboxyl groups, together with the bending angle of 120° in the PDDB, generates a void inside the TSH, which is functionalized by the pyridinic ring at the center of PDDBs. Dimethylammonium ions, which are present in the solid state of discrete TSHs, neutralize the charge of TSHs and stabilize the solid structure with hydrogen bonding. Large-sized TSHs possess high connectivity and proper symmetry for constructing a 2D hierarchical coordination framework, which is a rare coordination platform obtained using the supermolecular building block (SBB) approach. The conversion of discrete TSHs into a 2D framework illustrates the suitability of discrete TSHs as SBBs for constructing higher-order coordination-driven frameworks.