Stacked nickelocenes: synthesis, structural characterization, and magnetic properties

Area of Science:

• Organometallic Chemistry
• Supramolecular Chemistry
• Magnetochemistry

Background:

• 1,8-diiodonaphthalene serves as a precursor for novel molecular architectures.
• Cyclopentadienyl nucleophiles enable the synthesis of complex organic frameworks.
• Nickelocene derivatives are known for their interesting electronic and magnetic properties.

Purpose of the Study:

• To synthesize and characterize a novel paramagnetic bisnickelocene derivative.
• To investigate the electronic interactions and magnetic properties of the synthesized compound.
• To elucidate the ground state electronic configuration through experimental and computational methods.

Main Methods:

• Diels-Alder and retro-Diels-Alder reactions for molecular construction.
• X-ray structure analysis for structural determination.
• Cyclic voltammetry, variable temperature paramagnetic 1H NMR spectroscopy, Evans method, magnetic susceptibility measurements, and density functional theory (DFT) calculations for property analysis.

Main Results:

• Synthesis of a bisnickelocene derivative (4) featuring a 1,8-naphthalene clamp.
• X-ray analysis confirmed a stacked arrangement of the two nickelocene units.
• Cyclic voltammetry indicated five accessible oxidation states (+4 to 0).
• Variable temperature NMR and magnetic susceptibility measurements demonstrated Curie-Weiss behavior and antiferromagnetic coupling (J = -31.49 cm(-1)).
• DFT calculations supported an open shell singlet ground state with four antiferromagnetically coupled electrons.

Conclusions:

• The synthesized bisnickelocene derivative exhibits significant electronic interaction between the nickel centers.
• The compound displays complex magnetic behavior consistent with antiferromagnetic coupling.
• The study provides insights into the structure-property relationships of stacked metallocene systems.