Ionic liquids based on FeCl(3) and FeCl(2). Raman scattering and ab initio calculations.

Area of Science:

• Materials Science
• Inorganic Chemistry
• Computational Chemistry

Background:

• Ionic liquids (ILs) offer tunable properties for various applications.
• Iron-containing ILs are of interest due to iron's unique chemistry.
• Understanding the speciation in these ILs is crucial for their development.

Purpose of the Study:

• To synthesize and characterize novel ionic liquids incorporating iron(II) and iron(III) chlorides.
• To determine the predominant iron-containing species in these ionic liquids.
• To investigate the structural and vibrational properties of these species using computational methods.

Main Methods:

• Preparation of ionic liquids by mixing iron(II) chloride or iron(III) chloride with 1-butyl-3-methylimidazolium chloride (BMIC).
• Raman scattering spectroscopy to identify iron-containing species.
• Ab initio calculations, including Hartree-Fock and density functional theory (DFT), to compute structures and vibrational spectra.
• Analysis using all-electron (6-31G) and effective core potential (LANL2DZ, CEP-31G) basis sets.

Main Results:

• Iron(II) chloride forms ILs with BMIC, predominantly yielding FeCl(4)(2-).
• Iron(III) chloride forms ILs with BMIC, forming FeCl(4-) when BMIC is in excess.
• Fe(2)Cl(7-) species were observed when iron(III) chloride was in excess.
• Optimized structures and vibrational spectra of the identified species were computed.

Conclusions:

• The study successfully prepared and characterized novel iron-based ionic liquids.
• The predominant iron-containing species were identified as FeCl(4)(2-), FeCl(4-), and Fe(2)Cl(7-) depending on the iron oxidation state and molar ratios.
• Computational methods provide valuable insights into the structure and bonding of these ionic liquid species.