π-π stacking, spin density and magnetic coupling strength

Area of Science:

• Materials Science
• Solid State Chemistry
• Quantum Chemistry

Background:

• Pi-pi stacking interactions are crucial intermolecular forces.
• Their role in magnetic properties, particularly magnetic coupling strength, is an area of ongoing research.
• The influence of spin density on this interaction remains experimentally and theoretically unconfirmed.

Purpose of the Study:

• To investigate the relationship between spin density and magnetic coupling strength in pi-pi stacking systems.
• To experimentally confirm the role of spin density in determining magnetic properties.
• To establish guidelines for predicting magnetic coupling strength based on spin density and contact distance.

Main Methods:

• Analysis of magnetostructural data from seven unpublished Cu(II) complexes.
• Compilation and analysis of data from ten previously reported radical systems.
• Correlation of spin density on short-contact atoms with observed magnetic coupling strengths.

Main Results:

• Confirmed that spin density on short-contact atoms is a major factor in pi-pi stacking magnetic coupling strength.
• Established thresholds for spin density and contact distance (e.g., C···C > 3.4 Å requires spin density > 0.1350 for significant coupling).
• Observed that decreasing contact distance with temperature increases spin density, enhancing magnetic coupling.

Conclusions:

• Spin density is a critical determinant of magnetic coupling strength in pi-pi stacking systems.
• Specific spin density values and contact distances are necessary for achieving medium to strong magnetic coupling.
• Low spin densities on short-contact atoms are identified as the primary reason for weak magnetic coupling in the studied complexes.