Gas Phase UV Spectrum of a Cu(II)–Bis(benzene) Sandwich Complex: Experiment and Theory

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.

Electronic Transitions in Different Redox States of Trinuclear 5,6,11,12,17,18‐Hexaazatrinaphthylene‐Bridged Titanium Complexes: Spectroelectrochemistry and Quantum Chemistry

“…A correct description of electronic excitations with a spincontaminated wave function has already been observed in the literature. [31] Nevertheless, the results of DFT shown here should be interpreted with reservations due to the high spin contamination of the system.…”

Performance of TD-DFT for Excited States of Open-Shell Transition Metal Compounds

“…Absorption Spectrum of [Cu(C 6 H 6 ) 2 ] 2+ . Having calibrated the performance of X-TD-DFT for the excited states of prototypical transition metal compounds, we now apply it to the absorption spectrum of [Cu(C 6 H 6 ) 2 ] 2+ , which was recorded recently by Cox et al 50 They also performed U-TD-DFT calculations to identify the transitions in the range of 36000− 46000 cm −1 . Although an overall agreement was observed between the theoretical and experimental spectra, there do exist some discrepancies in between, e.g., the experimental peak near 42500 cm −1 was not found by U-TD-DFT.…”

“…46−49 Another system, [Cu-(C 6 H 6 ) 2 ] 2+ , that goes beyond the capability of both MS-CASPT2 and ic-MRCISD was also considered in order to compare with the previous U-TD-DFT and experimental results. 50 After a brief description of the computational details in section 2, the calculated results are analyzed in depth in section 3. The account ends with concluding remarks in section 4.…”

Wavelength-Dependent Ultraviolet Photodissociation of Protonated Tryptamine

“…Ultraviolet photodissociation (UVPD) experiments can provide valuable information about fragmentation of electronically excited ions. − The method can be experimentally applied by the combination of a mass spectrometer and a UV laser. , Even under a fixed laser wavelength, valuable information about molecular structures and fragmentation pathways can be obtained. For example, Kang et al explored the photodissociation dynamics of protonated tryptophan, which was generated by electrospray ionization (ESI) by irradiation with a laser at 266 nm.…”