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Ch.21 - Transition Elements and Coordination Chemistry
Chapter 21, Problem 21.102

Draw a crystal field energy-level diagram for the 3d orbitals of titanium in [Ti(H2O)6]3+]. Indicate the crystal field splitting, and explain why is [Ti(H2O)6]3+] colored.

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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 how the arrangement of ligands around a central metal ion affects the energy levels of its d orbitals. In an octahedral complex like [Ti(H2O)6]3+, the d orbitals split into two sets: the lower-energy t2g and the higher-energy eg orbitals. This splitting occurs due to the electrostatic interactions between the negatively charged ligands and the positively charged metal ion.
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The study of ligand-metal interactions helped to form Ligand Field Theory which combines CFT with MO Theory.

Crystal Field Splitting Energy (Δ)

Crystal Field Splitting Energy (Δ) is the energy difference between the split d orbital sets in a coordination complex. The magnitude of Δ influences the electronic transitions of the metal ion, which in turn affects the color observed in the complex. A larger Δ typically results in different colors due to the specific wavelengths of light absorbed during these transitions.
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The crystal field splitting pattern for octahedral complexes has the d orbitals on or along the axes as having the higher energy.

Color in Transition Metal Complexes

The color of transition metal complexes, such as [Ti(H2O)6]3+, arises from the absorption of specific wavelengths of light that promote electrons from the lower-energy t2g orbitals to the higher-energy eg orbitals. The color observed is complementary to the color of light absorbed. For example, if the complex absorbs light in the red region, it will appear green, as green is the complementary color to red.
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Transition Metals
Related Practice
Textbook Question
In excess of NH3(aq), Zn2+ forms a complex ion, [Zn(NH3)4]2+ which has a formation constant Kf = 7.8 x 10^8. Calculate the concentration of Zn2+ in a solution prepared by adding 1.00 x 10^-2 mol Zn(NO3)2 to 1.00 L of 0.250 M NH3. (a) 7.9 x 10^-4 M (b) 2.8 x 10^-6 M (c) 3.9 x 10^-9 M (d) 6.4 x 10^-11 M
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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

What is the electron configuration of Co2+ and how many unpaired electrons are in the free transition metal ion?

(a) [Ar]3d54s2; 5 unpaired electrons

(b) [Ar]3d54s2; 1 unpaired electron

(c) [Ar]3d7; 3 unpaired electrons

(d) [Ar]3d7; 1 unpaired electron

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Textbook Question

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.

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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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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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