Gas phase UV spectrum of a Cu(II)-bis(benzene) sandwich complex: experiment and theory

J Phys Chem A. 2014 Nov 13;118(45):10730-7. doi: 10.1021/jp506530g. Epub 2014 Nov 3.

Abstract

Photofragmentation with tunable UV radiation has been used to generate a spectrum for the copper-bis(benzene) complex, [Cu(C6H6)2](2+), in the gas phase. The ions were held in an ion trap where their temperature was reduced to ∼150 K, whereby the spectrum revealed two broad features at ∼38,200 and ∼45,700 cm(-1). Detailed calculations using density functional theory (DFT) show the complex can occupy three minimum energy structures with C2v and C2 (staggered and eclipsed) symmetries. Adiabatic time-dependent DFT (TDDFT) has been used to identify electronic transitions in [Cu(benzene)2](2+), and the calculations show these to fall into two groups that are in excellent agreement with the experimental data. However, the open-shell electronic configuration of Cu(2+) (d(9)) may give rise to excited states with double-excitation character, and the single-excitation adiabatic TDDFT treatment leads to extensive spin contamination. By quantifying the extent of spin contamination and allowing for the inclusion of a small percentage (∼10%), the theory can provide quantitative agreement with the experimental data.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Benzene / chemistry*
  • Copper / chemistry*
  • Gases / chemistry*
  • Models, Chemical
  • Photochemical Processes
  • Spectrum Analysis
  • Ultraviolet Rays

Substances

  • Gases
  • Copper
  • Benzene