Abrupt spin transition in a modified-terpyridine cobalt(ii) complex with a highly-distorted [CoN₆] core

Area of Science:

• Inorganic Chemistry
• Materials Science
• Coordination Chemistry

Background:

• Spin transition (ST) and spin crossover (SCO) phenomena in metal complexes are crucial for developing molecular switches and memory devices.
• Cobalt(II) complexes with terpyridine ligands are known to exhibit spin crossover behavior.
• Understanding the relationship between molecular structure and spin transition properties is key for designing new functional materials.

Purpose of the Study:

• To synthesize and characterize a novel cobalt(II) complex with a π-conjugated substituent, [Co(Naph-C2-terpy)2](BF4)2.
• To investigate the spin transition behavior of the synthesized complex and its solvated derivative.
• To correlate the structural distortions of the cobalt(II) coordination core with the observed spin transition properties.

Main Methods:

• Synthesis of the cobalt(II) complex [Co(Naph-C2-terpy)2](BF4)2.
• Single crystal X-ray structural analysis of the complex and its solvated form.
• Characterization of spin transition behavior using appropriate techniques (e.g., temperature-dependent magnetic susceptibility measurements - implied).

Main Results:

• The non-solvated complex [Co(Naph-C2-terpy)2](BF4)2 exhibits abrupt spin transition (ST) with a cooperative factor of 0.91.
• The solvated product, 1·2MeOH, shows gradual spin crossover (SCO) behavior with a cooperative factor of 0.49.
• Single crystal X-ray analysis revealed a highly distorted octahedral [CoN6] coordination core in complex 1, which is stabilized by intermolecular interactions, leading to abrupt ST.

Conclusions:

• The degree of distortion in the [CoN6] core significantly influences the nature of the spin transition.
• Strong intermolecular interactions can stabilize a highly distorted coordination environment, promoting abrupt spin transition behavior.
• The study provides insights into the design principles for cobalt(II) complexes exhibiting controlled spin transition properties.