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Ch.21 - Transition Elements and Coordination Chemistry
McMurry - Chemistry 8th Edition
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Tutti i libri di testoMcMurry 8th EditionCh.21 - Transition Elements and Coordination ChemistryProblema 21.134c
Capitolo 21, Problema 21.134c

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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Identify the oxidation state of iron in the complex [Fe(C2O4)3]3-. Since the overall charge of the complex is -3 and each oxalate (C2O4)2- ligand contributes -2, the iron must be in the +3 oxidation state (Fe3+).
Recognize that oxalate (C2O4)2- is a bidentate ligand, meaning it coordinates twice with the central metal ion. This results in a coordination number of 6 for the iron ion, forming an octahedral geometry around the iron.
Understand that oxalate is a weak-field ligand according to the spectrochemical series. This influences the splitting of the d-orbitals in the crystal field theory, resulting in a smaller energy gap between the t2g and eg orbitals in an octahedral field.
Draw the crystal field splitting diagram for an octahedral complex with a weak-field ligand. Place the five d-electrons of Fe3+ into the diagram according to Hund's rule and the Aufbau principle, starting with the lower energy t2g orbitals and then moving to the higher energy eg orbitals.
Count the number of unpaired electrons based on the electron configuration in the energy-level diagram. This will help predict the magnetic properties of the complex.

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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 this theory, ligands create an electric field that splits the degenerate d-orbitals of the metal ion into different energy levels. The extent of this splitting depends on the nature of the ligands and their geometry, which is crucial for predicting the magnetic properties and color of coordination complexes.
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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 metal complex. Strong-field ligands cause a larger splitting of the d-orbitals, leading to lower energy configurations and potentially fewer unpaired electrons. Conversely, weak-field ligands, like oxalate in this case, result in smaller splitting, which can lead to more unpaired electrons and a higher magnetic moment.
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Strong-Field Ligands result in a large Δ and Weak-Field Ligands result in a small Δ.

Unpaired Electrons and Magnetism

The presence of unpaired electrons in a coordination complex is directly related to its magnetic properties. Complexes with unpaired electrons exhibit paramagnetism, meaning they are attracted to magnetic fields, while those with all paired electrons are diamagnetic and are not attracted to magnetic fields. The number of unpaired electrons can be determined from the crystal field energy-level diagram, which illustrates how the d-orbitals are filled based on the ligand field strength.
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Magnetic Quantum Example
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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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Domanda del libro di testo

What is the systematic name for each of the following ions? 

(c) [Co(CO3)3]3-

(d) [Pt(en)2(SCN)2]2+

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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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Domanda del libro di testo

For each of the following complexes, describe the bonding using valence bond theory. Include orbital diagrams for the free metal ion and the metal ion in the complex. Indicate which hybrid orbitals the metal ion uses for bonding, and specify the number of unpaired electrons. 

(b) [Ag(NH3)2]+

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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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Domanda del libro di testo

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.

(b) If NiCl2L2 is paramagnetic and Ni(NCS)2L2 is diamagnetic, which of the two complexes is tetrahedral and which is square planar?

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