Question

Read the passage carefully and answer the questions that follow.

Crystal field splitting by various ligands Metal complexes show different colours due to d-d transitions. The complex absorbs light of specific wavelength to promote the electron from t2g to eg level. The colour of the complex is due to the transmitted light, which is complementary of the colour absorbed. The wave number of light absorbed by different complexes of Cr ion are given below: Complex Wavenumber of light absorbed (cm-1) Energy of light absorbed (kJ/mol) [CrA6]3- 13,640 163 [CrB6]3+ 17,830 213 [CrC6]3+ 21,680 259 [CrD6]3- 26,280 314

Answer the following questions:

_(a) Out of ligands "A", "B", "C" and "D", which ligand causes maximum crystal field splitting? Why?

OR

Which of the two, “A” or “D” will be a weak field ligand? Why?

(b) Which of the complexes will be violet in colour? [CrA₆]^3- or [CrB₆]³⁺ and why?
(Given: If 560 - 570 nm of light is absorbed, the colour of the complex observed is violet.)

(c) If the ligands attached to Cr³⁺ ion in the complexes given in the table above are water, cyanide ion, chloride ion, and ammonia (not in this order).

Identify the ligand, write the formula and IUPAC name of the following:

1. [CrA₆]^3-
2. [CrC₆]³⁺

Answer 1

(a) D Energy is directly proportional to the wave number. Maximum energy of light is required for an electron to jump from t_2g to eg in case of [CrD₆]^3-.

OR

A, The splitting caused in least in this case as the energy required for electron to jump from t_2g to eg., is minimum.

(b) [CrB₆]³⁺, wavelength of light absorbed is `1/17830 = 560` nm for the complex while `1/13640` = 733 nm for [CrA₆]^3- complex.

(c) 

1. [CrCl₆]^3-, Hexachloridochromate (III) ion
2. [Cr(NH₃)₆]³⁺, Hexaamminechromium (III) ion
   \[\ce{A = Cl-, B = H2O, C = NH3, D = CN-}\]