Question

The [VBr6]3- complex shows two absorption bands, i.e. at 6 600 cm-1, 13 000 cm-1 and 19 200 cm-1. Determine delta and the the interelectronic rrepulsion parameter, B, for this complex. Bfi = 930 cm-1. Use a d3 Tanabe-Sugano diagram for your solution. The x-axis is (delta/B) x 10, i.e. 10, 20, 30.

Answer 1

Here, there will be 3 transitions for V²⁺ ion, whose ground term is 4A_2g

Transition 1: 4A_2g 4T_2g, ₁ = = 19200 cm^-1 (lowest wavelength, i.e. highest energy or highest wavenumber)

Transition 2: 4A_2g 4T_1g(F), ₂ = 13000 cm^-1

Transition 3: 4A_2g 4T_1g(P), ₃ = 6600 cm^-1

B_freeion = B_fi = 930 cm^-1

15B = ₃ + ₂ - 3*₁ = 6600 + 13000 - (3*19200) = 38000 cm^-1

Therefore, the interelectronic repulsion parameter (B) = 38000/15 ~ 2533 cm^-1.

Now, the nephelauxetic ratio () = B/B_fi = 2533/930 = 2.7