Q.8 The octahedral metal oxide with the highest CFSE value is
(A) ZnO
(B) MnO
(C) VO
(D) TiO
Option Analysis
ZnO
Features wurtzite structure with tetrahedral coordination, not octahedral, so no CFSE applies. Zn²⁺ has d¹⁰ configuration, yielding zero CFSE even if octahedral.
MnO
Mn²⁺ (d⁵, high-spin) in octahedral field has t₂g³ eg² configuration. CFSE = (-0.4×3 + 0.6×2) Δo = 0, due to balanced filling.
VO
V²⁺ (d³) has t₂g³ configuration. CFSE = -0.4×3 Δo = -1.2 Δo, the maximum among options as early 3d metals with d³ provide high stabilization.
TiO
Ti²⁺ (d²) has t₂g² configuration. CFSE = -0.4×2 Δo = -0.8 Δo, lower than VO despite similar Δo influenced by higher charge/radius ratio.
CFSE Comparison Table
| Metal Oxide | Metal Ion | d Electrons | Configuration (High-Spin) | CFSE (in Δo units) |
|---|---|---|---|---|
| ZnO | Zn²⁺ | d¹⁰ | Not applicable | 0 |
| MnO | Mn²⁺ | d⁵ | t₂g³ eg² | 0 |
| VO | V²⁺ | d³ | t₂g³ | -1.2 |
| TiO | Ti²⁺ | d² | t₂g² | -0.8 |
VO shows the highest (most negative) CFSE, indicating greatest stability from crystal field effects.
Introduction
In coordination chemistry, the octahedral metal oxide with the highest CFSE value is a key topic for CSIR NET aspirants studying crystal field theory. This article breaks down CFSE for ZnO, MnO, VO, and TiO, explaining why one stands out in octahedral geometry with rock salt structures.
Crystal Field Theory Basics
Crystal field theory explains d-orbital splitting in octahedral fields into t₂g (lower) and eg (higher) sets, separated by Δo. CFSE quantifies stabilization, peaking at d³ configurations like -1.2 Δo for high-spin cases. Oxide ions (O²⁻) act as weak-field ligands, favoring high-spin.
Detailed CFSE Calculations
All oxides (except ZnO) have rock salt (NaCl-type) structures with M²⁺O²⁻ octahedral units. Δo increases left-to-right in 3d series due to higher charge density, but electron count dominates here.
- TiO (d²): -0.8 Δo
- VO (d³): -1.2 Δo (highest)
- MnO (d⁵): 0
- ZnO: No splitting (d¹⁰, tetrahedral preference)
Exam Relevance for CSIR NET
This question tests d-counts, high-spin assumptions, and structure identification. VO’s d³ yields unmatched CFSE, common in GATE/CSIR problems on transition metal oxides.
