Transition Metal Complexes with Appended Benzimidazole Groups for Sensing Dihydrogenphosphate

Area of Science:

• Coordination Chemistry
• Photophysics
• Supramolecular Chemistry

Background:

• Ruthenium, Rhenium, and Iridium complexes with bipyridine ligands are crucial in photophysical studies.
• Understanding anion interactions with metal complexes is key to developing new functional materials.

Purpose of the Study:

• To synthesize and characterize four new metal complexes: [Ru(bpy)2(bbib)](PF6)2, [Ru(phen)2(bbib)](PF6)2, [Re(CO)3(bbib)(py)](PF6), and [Ir(ppy)2(bbib)](PF6).
• To investigate the photophysical properties and anion-binding behavior of these complexes in various solvents.
• To elucidate the interaction mechanisms between the complexes and anions such as acetate and dihydrogenphosphate.

Main Methods:

• Synthesis and characterization of four novel metal complexes.
• Spectroscopic analysis (UV-Vis absorption, emission) to determine photophysical properties.
• NMR titrations (1H and 31P) to study anion interactions and complex speciation.
• X-ray crystallography to confirm solid-state structures.

Main Results:

• The bbib ligand exhibits redshifted absorptions upon interaction with acetate and dihydrogenphosphate anions.
• The 3MLCT emissive state is sensitive to anion concentration, showing quenching with acetate and variable behavior with dihydrogenphosphate.
• NMR studies indicate the imidazole group acts as both a proton acceptor and donor with dihydrogenphosphate.
• Complex equilibria involving dimeric {[complex]2-H2PO4} and bis(dihydrogenphosphate) species were observed, influenced by complex charge, ligand hydrophobicity, and solvent.

Conclusions:

• The synthesized metal complexes display distinct photophysical responses to anion binding.
• Dihydrogenphosphate interactions are complex, involving proton transfer and the formation of multiple supramolecular species.
• The observed speciation highlights the tunability of these complexes for potential applications in anion sensing or molecular recognition.