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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 21.136c
Chapter 21, Problem 21.136c

The percent iron in iron ore can be determined by dissolving the ore in acid, then reducing the iron to Fe2+, and finally titrating the Fe2+ with aqueous KMnO4. The reaction products are Fe2+ and Mn2+.
(c) Draw a crystal field energy-level diagram for the reactants and products, MnO4-, 3Fe1H2O2642+, 3Fe1H2O2643+, and 3Mn1H2O2642+, and predict the number of unpaired electrons for each.

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Identify the oxidation states of the central metal ions in each complex: Mn in \( \text{MnO}_4^- \) is in the +7 oxidation state, Fe in \( [\text{Fe(H}_2\text{O)}_6]^{2+} \) is in the +2 oxidation state, Fe in \( [\text{Fe(H}_2\text{O)}_6]^{3+} \) is in the +3 oxidation state, and Mn in \( [\text{Mn(H}_2\text{O)}_6]^{2+} \) is in the +2 oxidation state.
Determine the electron configuration for each metal ion: Mn in \( \text{MnO}_4^- \) has no d electrons, Fe in \( [\text{Fe(H}_2\text{O)}_6]^{2+} \) has a \( 3d^6 \) configuration, Fe in \( [\text{Fe(H}_2\text{O)}_6]^{3+} \) has a \( 3d^5 \) configuration, and Mn in \( [\text{Mn(H}_2\text{O)}_6]^{2+} \) has a \( 3d^5 \) configuration.
Draw the crystal field splitting diagrams for each complex: For \( [\text{Fe(H}_2\text{O)}_6]^{2+} \) and \( [\text{Fe(H}_2\text{O)}_6]^{3+} \), consider the octahedral field splitting of the d orbitals into \( t_{2g} \) and \( e_g \) levels. Similarly, draw the splitting for \( [\text{Mn(H}_2\text{O)}_6]^{2+} \).
Predict the number of unpaired electrons: For \( [\text{Fe(H}_2\text{O)}_6]^{2+} \), with a \( 3d^6 \) configuration, determine the distribution of electrons in the \( t_{2g} \) and \( e_g \) orbitals. For \( [\text{Fe(H}_2\text{O)}_6]^{3+} \) and \( [\text{Mn(H}_2\text{O)}_6]^{2+} \), with a \( 3d^5 \) configuration, determine the distribution of electrons in the \( t_{2g} \) and \( e_g \) orbitals.
Count the unpaired electrons for each complex based on the electron distribution in the crystal field diagrams.

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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 the electronic structure of transition metal complexes by considering the effect of surrounding ligands on the d-orbitals of the metal ion. 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 arrangement of electrons and the magnetic properties of the complex, including the number of unpaired electrons.

Titration and Redox Reactions

Titration is a quantitative analytical method used to determine the concentration of a solute in a solution. In this context, the titration involves a redox reaction where Fe2+ ions are oxidized to Fe3+ by KMnO4, which is reduced from MnO4- to Mn2+. Understanding the stoichiometry of this reaction is crucial for calculating the percent iron in the ore based on the volume of KMnO4 used.

Unpaired Electrons and Magnetic Properties

The presence of unpaired electrons in an atom or ion determines its magnetic properties. Transition metal complexes can exhibit paramagnetism if they have unpaired electrons, while those with all paired electrons are diamagnetic. By analyzing the electron configuration of the reactants and products in the given reaction, one can predict the number of unpaired electrons and thus infer the magnetic behavior of the complexes.
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Cobalt(III) trifluoroacetylacetonate, Co1tfac23, is a sixcoordinate, octahedral metal chelate in which three planar, bidentate tfac ligands are attached to a central Co atom:

(d) Draw a crystal field energy-level diagram for Co1tfac23, and predict its magnetic properties. (In this complex, tfac is a strong-field ligand.)

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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.

(c) [Co(NCS)4]2- (tetrahedral)

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Textbook Question

In acidic aqueous solution, the complex trans-[Co(en)2Cl1]2+(aq) undergoes the following substitution reaction:

trans-[Co(en)1Cl2]+(aq) + H2O(l) → trans-[Co(en)2(H2O)Cl]2+(aq) + Cl–(aq)

The reaction is first order in trans-[Co(en)2Cl2]+(aq), and the rate constant at 25°C is 3.2×10–5 s–1.

(d) Is the reaction product chiral or achiral? Explain.

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Textbook Question

Nickel(II) complexes with the formula NiX2L2, where X is Cl- or N-bonded NCS- and L is the monodentate triphenylphosphine ligand P(C6H5)3, can be square planar or tetrahedral.

(c) Draw possible structures for each of the NiX2L2 complexes, and tell which ones have a dipole moment.

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Textbook Question

Spinach contains a lot of iron but is not a good source of dietary iron because nearly all the iron is tied up in the oxalate complex [Fe(C2O4)3]3-.

(c) Draw a crystal field energy-level diagram for [Fe(C2O4)3]3-, and predict the number of unpaired electrons. (C2O42- is a weak-field bidentate ligand.)

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Textbook Question

In acidic aqueous solution, the complex trans-[Co(en)2Cl1]2+(aq) undergoes the following substitution reaction:

trans-[Co(en)2Cl1]+(aq) + H2O(l) → trans-[Co(en)2(H2O)Cl]2+(aq) + Cl–(aq)

The reaction is first order in trans-[Co(en)2Cl2]+(aq), and the rate constant at 25°C is 3.2×10–5 s–1.

e. Draw a crystal field energy-level diagram for trans-[Co(en)2Cl2]+ that takes account of the fact that Cl– is a weaker-field ligand than ethylenediamine.

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