Chapter 22.4, Problem 1PPC

Interpretation Introduction

Interpretation:

The colouring properties in thegiven coordination compounds are to be explained.

Concept introduction:

The sunlight comprises all the colors. The objects reflecting all these colors appear white and the objects absorbing all these colors appear black. Any object that absorbs all colors but reflects a particular color is said to possess that color.

The colour in coordination compounds can be explained on the basis of crystal field splitting energy by using the expressionbelow:

$\Delta E\text{(or simplyΔ)}=\text{h}\frac{\text{c}}{\text{λ}}$

Here, $\Delta E$ is the change in energy, $\text{c}$ is the speed of light, $\text{h}$ is Planck’s constant, and $\lambda$ is the wavelength of the photon.

The colour of a complex compound is the same as the magnitude of the energy of a photon of visible light. The transition metal complex absorbs the visible light, which causes the electron to jump from the lower energy $\text{d}$ orbital to the higher energy $\text{d}$ orbital.

Spectrochemical series: ${\text{I}}^{-}{\text{< Br}}^{-}{\text{< Cl}}^{-}{\text{< OH}}^{-}{\text{< F}}^{-}{\text{< H}}_2{\text{O < NH}}_3{\text{< en < CN}}^{-}\text{< CO}$

These ligands are arranged in order of increasing value of $\Delta E$.

${\text{CN}}^{-}$ and $\text{CO}$ are strong field ligands.

${\text{H}}_{\text{2}}\text{O}$ is weak field ligand.