Coordination Compounds

(a) This is a square planar complex of type MA B . Two geometrical isomers are possible: - **Cis-isomer:** both Cl ligands adjacent - **Trans-isomer:** Cl ligands opposite (b) Give the electronic configuration of ion when .
Solution:
(b) When , the ligand field is strong → **low-spin configuration**
(c) Solution of is green in colour, whereas is colourless. Give reason.
(Ni = 28) Solution:
(c) - In : Weak field ligand → octahedral, → partially filled d-orbitals → d-d transition allowed → green color. - In : Strong field ligand (CN ) → low-spin, square planar → all electrons paired → d-d transition not allowed → colourless.

(a) The reaction is a free radical halogenation at the benzylic position: (b) Toluene undergoes benzylic chlorination: Only one hydrogen is replaced at the benzylic position in monohalogenation.

Ligand field strength increases in the order: Excitation energy is directly related to the crystal field splitting energy , which is maximum for strong field ligands like CN . Therefore, complex with CN ligand will exhibit: - Maximum crystal field splitting - Highest excitation energy for d–d transition

The complex contains Ni in +2 oxidation state. Electronic configuration of Ni is: Cyanide (CN ) is a strong field ligand and causes pairing of electrons. Hence, the 3d electrons pair up and the complex becomes low-spin and diamagnetic (no unpaired electrons).
In such cases, the hybridization is , which leads to a square planar geometry.

Stability of complexes depends on factors like: - Nature of ligand (strong or weak field) - Chelate effect - Charge on central metal ion - Nature of metal Analysis: - (A) : Involves monodentate ligand (NH ) with moderate field strength. Stability is moderate.
- (B) : Contains only two ammonia ligands; silver(I) forms labile complexes. Low stability.
- (C) : Contains bidentate ethylenediamine ligands (en) which provide some chelation. However, presence of Cl weakens stability.
- (D) : Cyanide (CN ) is a strong field ligand forming very stable low-spin complexes with Fe(II). This makes it highly stable.
Therefore, the most stable complex is: