Alkyl halide charge transfer complexes with hard Lewis bases.

Area of Science:

• Physical Chemistry
• Spectroscopy
• Chemical Bonding

Background:

• Charge transfer complexes are typically formed between electron donors and acceptors.
• Alkyl halides as acceptors and amines/alcohols as donors in low dielectric solvents present an unusual system.
• Classical theories of charge transfer complexes often assume positive electron affinity for acceptors.

Purpose of the Study:

• To examine the formation and properties of unusual charge transfer complexes between alkyl halides and hard Lewis bases.
• To understand the spectral and thermodynamic characteristics of these complexes.
• To investigate their behavior in low dielectric solvents and compare them to classical charge transfer complexes.

Main Methods:

• Ultraviolet (UV) spectroscopy was employed to study the complexes.
• Thermodynamic analysis was used to probe complex formation equilibria.
• Concentration variation experiments were conducted.

Main Results:

• The maximum absorbance wavelength (lambda(max)) of the complexes decreased with increasing donor ionization potential.
• Complex formation was generally slightly exergonic with negative complexation entropy at ambient temperatures.
• Complex extinction coefficients were significantly lower than those of typical charge transfer complexes.
• These complexes displayed an atypical hypsochromic shift with increasing solvent dielectric constant, unusual for acceptors with negative electron affinity.

Conclusions:

• The studied alkyl halide-amine/alcohol complexes represent an extraordinary class of charge transfer interactions.
• Their spectral and thermodynamic properties deviate from classical charge transfer complex behavior.
• The findings challenge conventional understanding of charge transfer complex formation and characteristics.