Going Up the Ladder: Stacking Four 4,4'-Bipyridine Moieties within a Ti(IV)-Based Tetranuclear Architecture

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Biphenol-based ligands are effective for binding titanium(IV) centers.
• Nitrogen ligands stabilize titanium(IV) complexes and facilitate self-assembly.
• Ligand design is crucial for controlling the nuclearity and structure of metal complexes.

Purpose of the Study:

• To synthesize and characterize novel titanium(IV) complexes using biphenol-based ligands with varying flexibility.
• To investigate the influence of ligand torsional freedom on the self-assembly process and resulting complex nuclearity.
• To explore the structural and electronic properties of the self-assembled titanium(IV) complexes.

Main Methods:

• Synthesis of bis-2,2'-biphenol ligands incorporating a central 4,4'-bipyridine unit.
• Complexation reactions with titanium(IV) precursors.
• X-ray crystallography for structural determination.
• Density Functional Theory (DFT) calculations for mechanistic insights.

Main Results:

• A flexible ligand (3H4) formed a mononuclear titanium(IV) complex, Ti(3)(DMF)2.
• A more rigid ligand (4H4) assembled into a tetranuclear titanium(IV) complex, Ti4(4)2(4H)2(OEt)2.
• The tetranuclear complex featured stacked 4,4'-bipyridine units and a unique arrangement of TiO6 and TiO5N coordination environments.
• DFT studies indicated a dimetallic intermediate in the formation of the tetranuclear complex.

Conclusions:

• Ligand torsional freedom is a key determinant in the nuclearity of self-assembled titanium(IV) complexes.
• The study demonstrates precise control over supramolecular architecture through ligand design.
• The findings contribute to the understanding of self-assembly principles in coordination chemistry and the development of novel titanium-based materials.