Name of the following coordination entities and describe their structure:

(i) [Fe (CN)₆]^4-

(ii) [Cr (NH₃)₄Cl₂]⁺

(iii) [Ni (CN) ₄]^2-

(Atomic numbers Fe = 26. Cr = 24, Ni = 28

(i) [Fe (CN)₆]^4-

IUPAC name: Hexacyanoferrate (II)

Structure: Oxidation state of iron is + 2

Fe2+: Electronic configuration is 3d⁶ 4s° 4p°

Orbitals of Fe²⁺ ions:

As CN^- is a strong field ligand, it causes the pairing of unpaired 3d electrons

Since there are six ligands around the central metal ion, the most feasible hydrization is d²sp³.

d²sp² hybridized orbitals of Fe²⁺ are:

6 electron pairs from CN^-1 ions occupy the six hybrid d²sp³ orbitals

Then,

Hence, the structure of [Fe (CN)₆]^4- is octahedral.

(ii) [Cr (NH₃)₄Cl₂] ⁺

Name: Tetraamminedichlorido chromium (III)

Electronic configuration of Cr: 3d⁴ 4s²

Electronic configuration of Cr³⁺: 3d³

Structure is octahedral with d²sp³ hybridization.

(iii) [Ni (CN) ₄]^2-

Name: Tetracyanonickelate (II)

Structure: Here oxidation state of Ni is + 2

Ni + 2: Electronic configuration is 3d⁸ 4s⁰ 4p⁰

Orbitals of Ni²⁺ ion

As CN^-1is a strong field ligand, it causes the pairing of unpaired 3d electrons.

Since, there are four ligands around the central metal ion, the most feasible hybridization is dsp²

4 electron pairs from CN^-1 ions occupy the four hybrid dsp2 orbitals

Then,

Hence, the structure of [Ni(CN)₄]^2- is square planar.