Electronic absorption spectrum of nickel acetate tetrahydrate

Abstract

The absorption spectrum of Ni(CH₃COO)₂·4H₂O has been studied at room temperature and at liquid nitrogen temperature. The interesting feature of the observed spectrum is the appearance of a double-peaked red band similar to those observed in aqueous solution and hexahydrated crystals of Ni²⁺. The various possible assignments of this red band are examined and the most likely assignment is found to be such that the lower wavelength peak corresponds to the transition to the ¹E(D) level, while the higher wavelength peak corresponds to the ³T₁(F) level. This assignment is confirmed by calculating the positions of these levels in the cubic field approximation with the values of the parameters B = 975 cm⁻¹, C = 4B, and Dq = 845 cm⁻¹ obtained from the positions of other observed bands. The fit obtained with the positions of the two respective peaks is found to be quite good. The spin-forbidden transition to the ¹E state borrows its intensity through the mixing of the triplet character into the state and, by solving the spin-orbit matrices, it is found that the Γ₃ (¹E) state does contain an appreciable amount of triplet character (35%).