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Ch.21 - Transition Elements and Coordination Chemistry
McMurry - Chemistry 8th Edition
McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook
All textbooksMcMurry 8th EditionCh.21 - Transition Elements and Coordination ChemistryProblem 21.133
Chapter 21, Problem 21.133

The amount of paramagnetism for a first-series transition metal complex is related approximately to its spin-only magnetic moment. The spin-only value of the magnetic moment in units of Bohr magnetons (BM) is given by sqrt(n(n + 2)), where n is the number of unpaired electrons. Calculate the spin-only value of the magnetic moment for the 2+ ions of the first-series transition metals (except Sc) in octahedral complexes with (a) weak-field ligands and (b) strong-field ligands. For which electron configurations can the magnetic moment distinguish between high-spin and low-spin electron configurations?

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1
Identify the first-series transition metals, which range from Titanium (Ti) to Zinc (Zn). Exclude Scandium (Sc) as per the problem statement.
Determine the electron configuration for each 2+ ion of these transition metals. This involves removing two electrons from the neutral atom's electron configuration, typically from the 4s orbital first, followed by the 3d orbital if necessary.
For each 2+ ion, calculate the number of unpaired electrons (n) in both weak-field (high-spin) and strong-field (low-spin) octahedral complexes. Weak-field ligands do not cause significant splitting of the d-orbitals, leading to more unpaired electrons, while strong-field ligands cause greater splitting, potentially leading to paired electrons.
Use the formula for the spin-only magnetic moment, \( \mu = \sqrt{n(n + 2)} \), to calculate the magnetic moment for each ion in both high-spin and low-spin configurations.
Identify which electron configurations result in different magnetic moments for high-spin and low-spin states. This occurs when the number of unpaired electrons differs between the two configurations, allowing the magnetic moment to distinguish between them.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Paramagnetism

Paramagnetism is a form of magnetism that occurs in materials with unpaired electrons. These unpaired electrons create a net magnetic moment, allowing the material to be attracted to an external magnetic field. In transition metal complexes, the presence of unpaired electrons is crucial for determining the magnetic properties, which can be quantified using the spin-only magnetic moment formula.
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Spin-Only Magnetic Moment

The spin-only magnetic moment is a theoretical calculation used to estimate the magnetic behavior of transition metal complexes based solely on the number of unpaired electrons. It is expressed in Bohr magnetons (BM) and calculated using the formula sqrt(n(n + 2)), where n represents the number of unpaired electrons. This value helps distinguish between different spin states in coordination complexes.
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High-Spin vs. Low-Spin Configurations

High-spin and low-spin configurations refer to the arrangement of electrons in d-orbitals of transition metal complexes in the presence of ligands. Weak-field ligands typically lead to high-spin configurations, where electrons occupy higher energy orbitals to minimize repulsion, resulting in more unpaired electrons. In contrast, strong-field ligands cause low-spin configurations, where electrons pair up in lower energy orbitals, leading to fewer unpaired electrons and a lower magnetic moment.
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Related Practice
Textbook Question

What is a racemic mixture? Does it affect plane-polarized light? Explain.

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Textbook Question

Draw a crystal field energy-level diagram, assign the electrons to orbitals, and predict the number of unpaired electrons for each of the following.

(a) [Cu(en)3]2+

(b) [FeF6]2-

(c) [Co(en)3]3+ (low spin) 

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Textbook Question

Which of the following complexes are paramagnetic?

(a) [Mn(CN)6]3-

(b) [Zn(NH3)4]2+ (tetrahedral)

(c) [Fe(CN)6]4-

(d) [FeF6]4-

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Textbook Question

Based on the wavelength of maximum absorption of the cobalt complexes, arrange the following ligands in a spectrochemical series from weakest-field to strongest-field ligand. 

(a) Cl- < NCS- < H2O < NH3 

(b) Cl- < NCS- < H2O < NH3 

(c) H2O < Cl- < NH3 < NCS-

(d) Cl- < H2O < NCS- < NH3

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Textbook Question

What hybrid orbitals are used by the metal ion and how many unpaired electrons are present the complex ion [VCl4]- with tetrahedral geometry?

(a) sp3; 2 unpaired electrons

(b) sp3; 3 unpaired electrons

(c) sp3d2; 3 unpaired electrons

(d) sp3d2; 4 unpaired electrons

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Textbook Question

For each of the following complexes, draw a crystal field energy-level diagram, assign the electrons to orbitals, and predict the number of unpaired electrons. 

(a) [CrF6]3-

(b) [V(H2O)6]3+

(c) [Fe(CN)6]3-

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