Coupled Excited States in Nickel(II) Complexes Probed by Polarized Absorption Spectroscopy

Abstract

The absorption spectra of Ni(H2O)6 2+, trans-NiCl2(H2O)4, and NiCl6 4- show an unusual band shape for the 3A2g → 3T1g, 1Eg (O h labels) electronic transitions in the near-infrared to visible wavelength range. A barely resolved broad band and an intense vibronic progression with a spacing larger than the totally symmetric ground-state metal−ligand vibrational frequency are superposed. Low-temperature polarized spectra are analyzed with a quantitative model and both the large interval and the band intensities are shown to arise from efficient intersystem crossings between the two excited states. Alternative assignments proposed in the literature are examined.

Zero-field splitting in nickel(II) complexes: A comparison of DFT and multi-configurational wavefunction calculations

“…This is in reasonable agreement with the experimental maximum of the lowest band in the absorption spectrum of aqueous nickel(II), occurring at about 7500 cm −1 . 74 We also notice that the agreement with experimental data improves in the MD snapshots. Table IV and shown in the right-hand side of Figure 4.…”

Allowed and Forbidden d-d Bands in Octahedral Coordination Compounds: Intensity Borrowing and Interference Dips in Absorption Spectra

“…(3), showing again the typical up-down-up difference trace, as given in Fig. 7b, and values of the fit parameters close to those obtained for Ni(H 2 O) 6 2+ determined before both from solution spectra and from better resolved single-crystal spectra [29,32].…”

“…Numerical models based on the time-dependent theory of electronic spectroscopy have been applied to a variety of spectra arising from transitions to coupled final states [6][7][8][30][31][32]. This approach is exact, within the numerical limits of the wavepacket propagation method used [6], but is more difficult to apply than the analytical equation presented above.…”

“…Figure 7 shows that the analytical equation can also be applied to crossings of the lowest-energy singlet excited state and the 3 T 1g ( 3 F) state. The best studied case of the interaction between these two states is the spectrum of Ni(H 2 O) 6 2+ [1,2,10,32,[40][41][42][43], another complex where Jørgensen contributed pioneering spectroscopic work. The Ni(dimethylsulfoxide) 6 2+ complex has band maxima at energies similar to Ni(H 2 O) 6 2+ , as expected from the identical ligator atoms.…”

The stability of aqueous nickel(II) chloride complexes in hydrothermal solutions: Results of UV–Visible spectroscopic experiments

“…As a first-row transition metal, aqueous Ni 2+ displays a typical octahedral structure with six water ligands in the first coordination shell (e.g., [Ni(H 2 O) 6 ] 2+ ; for simplicity the water ligand is not shown for nickel species in the rest of this paper). With a d 8 electronic configuration, the ground state ( 3 A 2g ) of the Ni ion in an octahedral field will have three major spin-allowed transitions (e.g., Cotton and Wilkinson, 1988;Bussière and Reber, 1998) Fig. 1.…”