Textbook Question
In octahedral complexes, the choice between high-spin and low-spin electron configurations arises only for d4 - d7 complexes. Explain.
Ch.21 - Transition Elements and Coordination Chemistry
Chapter 21, Problem 118
Draw a crystal field energy-level diagram, and predict the number of unpaired electrons for each of the following: (c) [FeO4]2-; (b) [Ru(NH3)6]2+ (low spin).
Verified step by step guidance1
Step 1: Identify the oxidation state of the metal in each complex. For [FeO4]2-, determine the oxidation state of Fe, and for [Ru(NH3)6]2+, determine the oxidation state of Ru.
Step 2: Determine the electron configuration of the metal ion in its oxidation state. For example, Fe in [FeO4]2- and Ru in [Ru(NH3)6]2+.
Step 3: For [FeO4]2-, consider the tetrahedral crystal field splitting. In tetrahedral fields, the d-orbitals split into two sets: e (lower energy) and t2 (higher energy). Arrange the electrons according to this splitting.
Step 4: For [Ru(NH3)6]2+, consider the octahedral crystal field splitting. In low-spin complexes, the d-orbitals split into two sets: t2g (lower energy) and eg (higher energy). Arrange the electrons according to this splitting, keeping in mind the low-spin nature.
Step 5: Count the number of unpaired electrons in each complex based on the electron arrangement in the crystal field diagrams. This will help predict the magnetic properties of the complexes.
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 d-orbital energies. In an octahedral field, for example, the d-orbitals split into two energy levels: the lower-energy t2g and the higher-energy eg. This splitting influences the electronic configuration of the metal ion, determining its magnetic properties and the number of unpaired electrons.
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01:18
The study of ligand-metal interactions helped to form Ligand Field Theory which combines CFT with MO Theory.
Ligand Field Strength
Ligand field strength refers to the ability of a ligand to influence the energy levels of the d-orbitals in a transition metal complex. Strong field ligands, like NH3, cause a larger splitting of the d-orbitals, often leading to low-spin configurations with fewer unpaired electrons. Conversely, weak field ligands result in smaller splitting and can lead to high-spin configurations with more unpaired electrons.
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02:40Strong-Field Ligands result in a large Δ and Weak-Field Ligands result in a small Δ.
Electron Configuration and Spin States
The electron configuration of a transition metal complex determines the distribution of electrons among the available d-orbitals. The spin state (high-spin or low-spin) is influenced by the ligand field strength and affects the number of unpaired electrons. High-spin complexes have more unpaired electrons due to less energy separation between the orbitals, while low-spin complexes have fewer unpaired electrons due to greater energy separation.
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01:32Ground State Electron Configurations
Related Practice
Textbook Question
For each of the following, (i) give the systematic name of the compound and specify the oxidation state of the transition metal, (ii) draw a crystal field energy-level diagram and assign the d electrons to orbitals, (iii) indicate whether the complex is high-spin or low-spin (for d4 - d7 complexes), and (iv) specify the number of unpaired electrons.
(a) (NH4)[Cr(H2O)6](SO4)2
Textbook Question
For each of the following, (i) give the systematic name of the compound and specify the oxidation state of the transition metal, (ii) draw a crystal field energy-level diagram and assign the d electrons to orbitals, (iii) indicate whether the complex is high-spin or low-spin (for d4 - d7 complexes), and (iv) specify the number of unpaired electrons.
(c) [Ni(NH3)4(H2O)2](NO3)2
Textbook Question
For each of the following, (i) give the systematic name of the compound and specify the oxidation state of the transition metal, (ii) draw a crystal field energy-level diagram and assign the d electrons to orbitals, (iii) indicate whether the complex is high-spin or low-spin (for d4 - d7 complexes), and (iv) specify the number of unpaired electrons. (d) K4[Os(CN)6]