Understand crystal field theory, splitting patterns, and crystal field stabilisation energy (CFSE). Includes practice questions to reinforce learning.
From the spectrochemical series (Cl− < F− < NH₃ < CN−), Cl− is the weakest field ligand, causing the smallest Δt.
Ref: NCERT Class 12 Chemistry > Chapter 5: Coordination Compounds > Topic: Crystal Field Theory - CFT and Crystal Field Splitting and CFSE
[Ni(CN)4]2− (Ni₂+, d8) with strong field CN− adopts square planar geometry, unlike tetrahedral with weak field ligands.
Ref: NCERT Class 12 Chemistry > Chapter 5: Coordination Compounds > Topic: Crystal Field Theory - CFT and Crystal Field Splitting and CFSE
Cr₂+ with 5 NH₃ and 1 Cl− (6 ligands). EAN = 24 − 2 + 2 × 6 = 34.
Ref: NCERT Class 12 Chemistry > Chapter 5: Coordination Compounds > Topic: Crystal Field Theory - CFT and Crystal Field Splitting and CFSE
In [Co(H₂O)6]SO₄, H₂O is neutral, and SO₄₂− has a −2 charge. The complex [Co(H₂O)6]2+ balances this, so Co’s oxidation state is +2.
Ref: NCERT Class 12 Chemistry > Chapter 5: Coordination Compounds > Topic: Crystal Field Theory - CFT and Crystal Field Splitting and CFSE
[Ni(H₂O)6]2+ (Ni₂+, d8) in an octahedral field undergoes d-d transitions, absorbing visible light (green color).
Ref: NCERT Class 12 Chemistry > Chapter 5: Coordination Compounds > Topic: Crystal Field Theory - CFT and Crystal Field Splitting and CFSE
Fe₂+ with 2 en (4 donor atoms) and 2 H₂O (2 donor atoms), total 6 ligands. EAN = 26 − 2 + 2 × 6 = 36.
Ref: NCERT Class 12 Chemistry > Chapter 5: Coordination Compounds > Topic: Crystal Field Theory - CFT and Crystal Field Splitting and CFSE
Primary valence is the oxidation state. In [Ni(NH₃)6]Cl₂, NH₃ is neutral, and 2 Cl− balance [Ni(NH₃)6]2+, so Ni is +2.
Ref: NCERT Class 12 Chemistry > Chapter 5: Coordination Compounds > Topic: Crystal Field Theory - CFT and Crystal Field Splitting and CFSE
From the spectrochemical series (Cl− < H₂O < NH₃ < CN−), CN− is the strongest field ligand, causing the largest Δo.
Ref: NCERT Class 12 Chemistry > Chapter 5: Coordination Compounds > Topic: Crystal Field Theory - CFT and Crystal Field Splitting and CFSE
Δo depends on ligand strength (spectrochemical series: CN− > NH₃ > H₂O > F−). [Co(CN)6]3− with strong field CN− has the highest Δo.
Ref: NCERT Class 12 Chemistry > Chapter 5: Coordination Compounds > Topic: Crystal Field Theory - CFT and Crystal Field Splitting and CFSE
[NiCl₄]2− (Ni₂+, d8) is tetrahedral with weak field Cl−. With strong field CN−, it becomes [Ni(CN)4]2−, square planar.
Ref: NCERT Class 12 Chemistry > Chapter 5: Coordination Compounds > Topic: Crystal Field Theory - CFT and Crystal Field Splitting and CFSE
[Mn(H₂O)6]2+ (Mn₂+, d5) with weak field H₂O is high spin (t2g3 eg2), 5 unpaired electrons, the maximum among options.
Ref: NCERT Class 12 Chemistry > Chapter 5: Coordination Compounds > Topic: Crystal Field Theory - CFT and Crystal Field Splitting and CFSE
[Cu(H₂O)4]2+ (Cu₂+, d9) undergoes a d-d transition in its square planar field, absorbing visible light (blue color), unlike [Ni(CO)4] (d10, no transition).
Ref: NCERT Class 12 Chemistry > Chapter 5: Coordination Compounds > Topic: Crystal Field Theory - CFT and Crystal Field Splitting and CFSE
