Strong π-Backbonding Enables Record Magnetic Exchange Coupling Through Cyanide

Area of Science:

• Inorganic Chemistry
• Materials Science
• Magnetochemistry

Background:

• Paramagnetic cyano-bridged complexes are of interest for their magnetic properties.
• Understanding electron delocalization in such complexes is crucial for tuning magnetic exchange interactions.

Purpose of the Study:

• To synthesize and characterize a novel paramagnetic cyano-bridged complex.
• To investigate the magnetic exchange coupling and electronic structure of the complex.
• To explore the role of low-coordinate metal fragments in mediating magnetic interactions.

Main Methods:

• Synthesis of a four-coordinate iron(II) monocyanide complex and a three-coordinate molybdenum(III) complex.
• X-ray diffraction and IR spectroscopy for structural and bonding analysis.
• Direct current (dc) magnetic susceptibility measurements.
• Electronic structure calculations.

Main Results:

• Successful assembly of the paramagnetic complex PhB(tBuIm)3Fe-NC-Mo(NtBuAr)3.
• X-ray diffraction and IR spectroscopy indicated delocalization of unpaired electron density into cyanide π* orbitals, reducing C-N bond order.
• Magnetic susceptibility measurements revealed strong antiferromagnetic exchange with J = -122(2) cm⁻¹, the strongest observed through cyanide.
• Electronic structure calculations supported the experimental findings.

Conclusions:

• The study demonstrates the strongest magnetic exchange coupling through cyanide to date.
• Low-coordinate metal fragments can induce exceptionally strong magnetic exchange via π-backbonding into the cyanide ligand.
• This work opens avenues for designing novel magnetic materials with tunable properties.