Question

(i)[Ni(CN)₄]²⁻ and [Ni(CO)(_4)] have different structures, but do not differ in their magnetic behaviour. Explain. 
(ii) Write the formula of Tetraamineaquachloridocobalt(III)chloride.

• A.
• B.
• C.
• D.

Hint:

Strong field ligands like CN(-) and CO almost always result in diamagnetic complexes with Nickel by forcing electron pairing!

Answer 1

The Correct Option is A

Concept:
Valence Bond Theory (VBT) explains the geometry and magnetic properties of coordination compounds based on hybridization. Strong field ligands such as CN− and CO cause pairing of electrons.

Step 1: Analyzing [Ni(CN)4]2−.
Ni is in +2 oxidation state (3d8). CN− is a strong field ligand and pairs the 3d electrons, leaving one 3d orbital vacant. Hybridization is dsp2 (square planar). Since all electrons are paired, the complex is diamagnetic.

Step 2: Analyzing [Ni(CO)4].
Ni is in 0 oxidation state (3d8 4s2). Strong field ligand CO forces 4s electrons into 3d orbitals, resulting in a 3d10 configuration. Hybridization is sp3 (tetrahedral). Since all electrons are paired, the complex is diamagnetic.

Step 3: Writing the Coordination Formula.
Central metal: Cobalt (Co)
Ligands: 4 Ammine (NH3), 1 Aqua (H2O), 1 Chlorido (Cl)

Oxidation state of Co is +3.
Total charge inside bracket = +3 + 4(0) + 1(0) + 1(-1) = +2.

To balance +2 charge, two chloride ions are present outside the coordination sphere.

Formula: [Co(NH3)4(H2O)Cl]Cl2