Textbook Question
Complete the exercises below. Draw the crystal-field energy-level diagrams and show the placement of electrons for each of the following complexes:
a. [VCl6]3–,
b. [FeF6]3– (a high-spin complex),
Ch.23 - Transition Metals and Coordination Chemistry
Chapter 23, Problem 66
Complete the exercises below. The ion [Fe(CN)₆]³⁻ has one unpaired electron, whereas [Fe(NCS)₆]³⁻ has five unpaired electrons. From these results, what can you conclude about whether each complex is high spin or low spin? What can you say about the placement of NCS⁻ in the spectrochemical series?
Verified step by step guidance1
Step 1: Understand the concept of high spin and low spin complexes. High spin complexes have a maximum number of unpaired electrons due to weak field ligands, while low spin complexes have fewer unpaired electrons due to strong field ligands.
Step 2: Analyze the electronic configuration of the central metal ion, Fe³⁺, which has a d⁵ configuration. In an octahedral field, the d orbitals split into two sets: t₂g (lower energy) and eₙ (higher energy).
Step 3: For [Fe(CN)₆]³⁻, note that CN⁻ is a strong field ligand, which typically leads to a low spin configuration. This means electrons will pair up in the lower energy t₂g orbitals before occupying the higher energy eₙ orbitals, resulting in fewer unpaired electrons.
Step 4: For [Fe(NCS)₆]³⁻, observe that NCS⁻ is a weaker field ligand compared to CN⁻. This suggests a high spin configuration, where electrons will occupy the eₙ orbitals before pairing in the t₂g orbitals, resulting in more unpaired electrons.
Step 5: Conclude that [Fe(CN)₆]³⁻ is a low spin complex with one unpaired electron, while [Fe(NCS)₆]³⁻ is a high spin complex with five unpaired electrons. This indicates that NCS⁻ is lower in the spectrochemical series compared to CN⁻.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Crystal Field Theory
Crystal Field Theory (CFT) explains how the arrangement of ligands around a central metal ion affects its electronic structure and energy levels. In octahedral complexes, the d-orbitals split into two energy levels: the lower-energy t2g and the higher-energy eg. The extent of this splitting is influenced by the nature of the ligands, determining whether electrons will pair up in the lower energy orbitals or occupy higher energy orbitals.
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01:18
The study of ligand-metal interactions helped to form Ligand Field Theory which combines CFT with MO Theory.
High Spin vs. Low Spin Complexes
High spin and low spin complexes refer to the arrangement of electrons in d-orbitals based on the strength of the ligands. High spin complexes have fewer paired electrons and result from weak field ligands that cause less splitting of d-orbitals, allowing electrons to occupy higher energy levels. Conversely, low spin complexes have more paired electrons due to strong field ligands that cause greater splitting, favoring electron pairing in the lower energy orbitals.
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01:28For octahedral complexes, Weak-Field Ligands create High-spin complexes and Strong-Field Ligands create Low-spin complexes.
Spectrochemical Series
The spectrochemical series is a list that ranks ligands based on their ability to split the d-orbitals of a metal ion. Strong field ligands, like CN⁻, cause large splitting and lead to low spin configurations, while weak field ligands, like I⁻, cause small splitting and favor high spin configurations. The position of NCS⁻ in this series indicates its relative strength as a ligand, influencing the electronic configuration and magnetic properties of the resulting complex.
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02:02Activity Series Chart
Related Practice
Textbook Question
Draw the crystal-field energy-level diagrams and show the placement of electrons for each of the following complexes:
d. [NiCl4]2+ (tetrahedral),
Textbook Question
Sketch the structure of the complex in each of the following compounds and give the full compound name:
a. cis-[Co(NH3)4(H2O)2] (NO3)2
Textbook Question
Sketch the structure of the complex in each of the following compounds and give the full compound name:
b. Na2[Ru(H2O)Cl5]