Textbook Question
Which of the following complexes are diamagnetic?
(a) [Ni(H2O)6]2+
(b) [Co(CN)6]3-
(c) [HgI4]2- (tetrahedral)
(d) [Cu(NH3)4]2+ (square planar)
Ch.21 - Transition Elements and Coordination Chemistry
McMurry8th EditionChemistryISBN: 9781292336145
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Table of contents
- Ch.1 - Chemical Tools: Experimentation & Measurement170
- Ch.2 - Atoms, Molecules & Ions160
- Ch.3 - Mass Relationships in Chemical Reactions169
- Ch.4 - Reactions in Aqueous Solution199
- Ch.5 - Periodicity & Electronic Structure of Atoms102
- Ch.6 - Ionic Compounds: Periodic Trends and Bonding Theory92
- Ch.7 - Covalent Bonding and Electron-Dot Structures61
- Ch.8 - Covalent Compounds: Bonding Theories and Molecular Structure59
- Ch.9 - Thermochemistry: Chemical Energy122
- Ch.10 - Gases: Their Properties & Behavior155
- Ch.11 - Liquids & Phase Changes54
- Ch.12 - Solids and Solid-State Materials73
- Ch.13 - Solutions & Their Properties120
- Ch.14 - Chemical Kinetics98
- Ch.15 - Chemical Equilibrium125
- Ch.16 - Aqueous Equilibria: Acids & Bases110
- Ch.17 - Applications of Aqueous Equilibria147
- Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium86
- Ch.19 - Electrochemistry154
- Ch.20 - Nuclear Chemistry96
- Ch.21 - Transition Elements and Coordination Chemistry156
- Ch.22 - The Main Group Elements187
- Ch.23 - Organic and Biological Chemistry51
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McMurry 8th EditionCh.21 - Transition Elements and Coordination ChemistryProblem 21.105
McMurry 8th EditionCh.21 - Transition Elements and Coordination ChemistryProblem 21.105Chapter 21, Problem 21.105
The [Cr(H2O)6]3+ ion is violet, and [Cr(CN)6]3- is yellow. Explain this difference using crystal field theory. Use the colors to order H2O and CN- in the spectrochemical series.
Verified step by step guidance1
Step 1: Understand that the color of a complex ion is due to the absorption of light which promotes an electron from a lower energy d-orbital to a higher energy d-orbital. The color we see is the complementary color of the light absorbed.
Step 2: Recognize that the crystal field theory explains the color of transition metal complexes in terms of the splitting of their d-orbitals into two sets of different energies when ligands approach the metal ion. The difference in energy between these two sets of d-orbitals corresponds to the energy of light absorbed.
Step 3: Realize that the extent of splitting of the d-orbitals, and hence the color of the complex, depends on the nature of the ligands. Ligands that cause a large splitting of the d-orbitals are known as strong-field ligands, while those that cause a small splitting are known as weak-field ligands.
Step 4: Infer from the given colors that [Cr(H2O)6]3+ absorbs light of higher energy (shorter wavelength) than [Cr(CN)6]3-. This is because violet light is the complementary color of yellow light, which is of lower energy (longer wavelength). Therefore, H2O is a weaker field ligand than CN-.
Step 5: Conclude that in the spectrochemical series, which orders ligands according to their ability to split the d-orbitals, H2O comes before CN-.
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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. When ligands approach the metal ion, they create an electric field that splits the degenerate d-orbitals into different energy levels. The extent of this splitting depends on the nature of the ligands and their arrangement around the metal ion.
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01:18
The study of ligand-metal interactions helped to form Ligand Field Theory which combines CFT with MO Theory.
Spectrochemical Series
The spectrochemical series is a list that ranks ligands based on the strength of the field they produce when coordinating to a metal ion. Strong field ligands, like CN<sup>-</sup>, cause a larger splitting of the d-orbitals, leading to higher energy transitions and different colors. Conversely, weak field ligands, such as H<sub>2</sub>O, result in smaller splitting and lower energy transitions, which can be observed in the color of the complexes.
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Color and d-Orbital Splitting
The color observed in transition metal complexes is a result of the specific wavelengths of light absorbed during electronic transitions between split d-orbitals. The energy difference between these orbitals corresponds to specific colors in the visible spectrum. For example, the violet color of [Cr(H<sub>2</sub>O)<sub>6</sub>]<sup>3+</sup> indicates that it absorbs light in the yellow-green region, while the yellow color of [Cr(CN)<sub>6</sub>]<sup>3-</sup> suggests it absorbs light in the violet region, reflecting the differences in ligand field strength.
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Related Practice
Textbook Question
What role does EDTA4- play as a trace additive to mayonnaise? Would the glycinate ion (H2NCH2CH2NH2) be an effective substitute for EDTA4-?
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.
(d) [Cu(en)2]2+ (square planar)
Textbook Question
Draw the structures of all possible diastereoisomers of an octahedral complex with the formula MA2B2C2. Which of the diastereoisomers, if any, can exist as enantiomers?
Textbook Question
Predict the crystal field energy-level diagram for a square pyramidal ML5 complex that has two ligands along the axes but only one ligand along the z axis. Your diagram should be intermediate between those for an octahedral ML6 complex and a square planar ML4 complex.
Textbook Question
Although Cl- is a weak-field ligand and CN- is a strong field ligand, [CrCl6]3- and [Cr(CN)6]3- exhibit approximately the same amount of paramagnetism. Explain.