In the following coordination compounds,1. [Fe(NH3)6]2+2. [Ni(CN)4]2-the electrons dont get paired even in the presence of a strong ligand.Why is it so?

Dear student,

When the geometry and the metal are held constant, the splitting of the d orbitals decreases in the following order.

CO

CN-

>

NO2-

>

NH3

>

-NCS-

>

H2O

>

OH-

F-

-SCN-

Cl-

>

Br-

strong-field ligands

weak-field ligands

Ligands that give rise to large differences between the energies of the t_2g and e_g orbitals are called strong-field ligands. Those at the opposite extreme are known as weak-field ligands.

Because they result from studies of the absorption spectra of transition-metal complexes, these generalizations are known as the spectrochemical series. The range of values of for a given geometry is remarkably large. The value of _o is 100 kJ/mol in the Ni(H₂O)₆²⁺ ion, for example, and 520 kJ/mol in the Rh(CN)₆^3- ion.

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