Angle-dependent electronic effects in 4,4'-bipyridine-bridged Ru3 triangle and Ru4 square complexes

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Electrochemistry

Background:

• Ruthenium complexes are vital in catalysis and materials science.
• Designing multinuclear metal complexes with specific geometries and redox properties is a key challenge.

Purpose of the Study:

• To synthesize and characterize novel redox-active ruthenium triangle and square complexes.
• To investigate the structural and electrochemical differences between these multinuclear complexes.

Main Methods:

• Synthesis of Ru3 triangle and Ru4 square complexes using 1,4,7,10-tetraazacyclododecane (cyclen) and 4,4'-bipyridine (4,4'-bpy) ligands.
• Crystal structure determination of the Ru3 triangle complex.
• Electrochemical analysis using cyclic voltammetry.
• Computational studies using Density Functional Theory (DFT).

Main Results:

• Assembly of a redox-active Ru3 triangle complex, [(cyclen)3Ru3(4,4'-bpy)3]Cl6.18H2O.THF, with bowed 4,4'-bpy ligands.
• Assembly of a Ru4 square complex, [(cyclen)4Ru4(4,4'-bpy)4](CF3SO3)8.2CF3SO3H.5MeOH.
• The Ru3 triangle complex exhibited three distinct one-electron oxidation events (0.207, 0.342, 0.434 V).
• The Ru4 square complex showed a single four-electron oxidation couple (0.430 V).
• DFT calculations indicated metal-based orbitals with contributions from 4,4'-bpy pi systems in the Ru3 triangle complex.

Conclusions:

• The geometry of bridging ligands significantly influences the redox behavior of multinuclear ruthenium complexes.
• The Ru3 triangle complex's structure facilitates stepwise electron transfer, while the Ru4 square complex allows for concerted electron transfer.
• These findings provide insights into the design of multinuclear complexes with tunable electronic properties.