[qquu50]

The spectrum of [Ni(Metu)6]2+ (Metu = N-methylythiourea) has peaks of moderate intensity at 8800, 13,100 and 19,800 cm-1.  Estimate the value of Dq and B.

[Alberto_Kravina]

The spectrum of [Ni(Metu)6]2+ (Metu = N-methylythiourea) has peaks of moderate intensity at 8800, 13,100 and 19,800 cm-1.  Estimate the value of Dq and B.

First of all you have to determine wether it's a high spin or low spin complex by looking at the number of allowed transitions, then, from the ratios of the energies of the various bands (e.g. E1/E2) you can look at which Dq/B' your transitions lie. The value for E/B is then read from the ordinate axis.

[Sossy]

Dear Alberto, Octahedral Ni²⁺, or d⁸ complexes cannot be low spin.

As to the value of Δ, the peak with the smallest wavenumber gives directly its value. It corresponds to ³A_2g  ³T_2g transition. To calculate B on the other hand, you need to use Tanabe Sugano diagram for d⁸ configuration. To do that, you have to take the ratios ν₂/ν₁, and ν₃/ν₁, move a vertical line along the horizontal axis, and find the position where the ratios are satisfied. Then read the values of the intersections of the terms with the vertical line along the vertical axis, expressed as ν/B. Now substitute the value of ν₁, ν₂, and ν₃ in the last formula using the numbers you read on the ν/B axis and you obtain B. Note that the three calculation results should agree.