Podcast
Questions and Answers
What does the Laporte selection rule state?
What does the Laporte selection rule state?
Only allowed transitions are those occurring with a change in parity or a change in the azimuthal quantum number by ±1.
Which of the following transitions is allowed according to the Laporte selection rule?
Which of the following transitions is allowed according to the Laporte selection rule?
- gerade to ungerade
- ungerade to gerade
- gerade to gerade
- Both A and B (correct)
The Laporte selection rule applies to tetrahedral complexes.
The Laporte selection rule applies to tetrahedral complexes.
False (B)
What does the Spin Selection rule state?
What does the Spin Selection rule state?
Which of the following mechanisms can allow 'forbidden' transitions to become somewhat 'allowed'?
Which of the following mechanisms can allow 'forbidden' transitions to become somewhat 'allowed'?
What happens to the center of symmetry during Vibronic Coupling?
What happens to the center of symmetry during Vibronic Coupling?
How do tetrahedral complexes affect color transitions?
How do tetrahedral complexes affect color transitions?
[Co(H2O)6]2+ is a type of _____ complex.
[Co(H2O)6]2+ is a type of _____ complex.
[CoCl4]2- exhibits a _____ color.
[CoCl4]2- exhibits a _____ color.
What is a characteristic of transitions that are allowed according to the Laporte selection rule?
What is a characteristic of transitions that are allowed according to the Laporte selection rule?
In terms of the azimuthal quantum number, what does the Laporte selection rule permit?
In terms of the azimuthal quantum number, what does the Laporte selection rule permit?
Which type of complexes does the Laporte selection rule not apply to?
Which type of complexes does the Laporte selection rule not apply to?
What is the restriction described by the Spin Selection rule?
What is the restriction described by the Spin Selection rule?
During an electronic transition, what must happen for the Laporte selection rule to apply?
During an electronic transition, what must happen for the Laporte selection rule to apply?
What is the resulting color of the tetrahedral complex [CoCl4]2-?
What is the resulting color of the tetrahedral complex [CoCl4]2-?
What is the effect of the absence of a center of symmetry in tetrahedral complexes?
What is the effect of the absence of a center of symmetry in tetrahedral complexes?
Which complex has a significantly higher transition intensity compared to [Co(H2O)6]2+?
Which complex has a significantly higher transition intensity compared to [Co(H2O)6]2+?
In which application has cobalt historically been used prior to 1400 BC?
In which application has cobalt historically been used prior to 1400 BC?
What characteristic of [Co(H2O)6]2+ leads to its relatively lower intensity in electronic transitions?
What characteristic of [Co(H2O)6]2+ leads to its relatively lower intensity in electronic transitions?
Which factor contributes to the visibility of colors in tetrahedral complexes?
Which factor contributes to the visibility of colors in tetrahedral complexes?
What is the typical range of values for transition intensity in the tetrahedral complex [CoCl4]2-?
What is the typical range of values for transition intensity in the tetrahedral complex [CoCl4]2-?
What occurs if the absorption for an octahedral complex falls in the ultraviolet range?
What occurs if the absorption for an octahedral complex falls in the ultraviolet range?
What is fluorescence?
What is fluorescence?
Which theory explains the colors of metal complexes?
Which theory explains the colors of metal complexes?
What is one major drawback of Crystal Field Theory?
What is one major drawback of Crystal Field Theory?
How are ligands classified in Crystal Field Theory?
How are ligands classified in Crystal Field Theory?
Which of the following complexes is expected to have the most intense color?
Which of the following complexes is expected to have the most intense color?
Which selection rule is primarily violated in spin-forbidden transitions?
Which selection rule is primarily violated in spin-forbidden transitions?
Which mechanism is involved in the temporary loss of center of symmetry during molecular vibrations?
Which mechanism is involved in the temporary loss of center of symmetry during molecular vibrations?
What characterizes the emission of light by fluorescent complexes when exposed to UV light?
What characterizes the emission of light by fluorescent complexes when exposed to UV light?
What phenomenon is not explained well by Crystal Field Theory?
What phenomenon is not explained well by Crystal Field Theory?
What is a consequence of the mixing of states in electronic transitions?
What is a consequence of the mixing of states in electronic transitions?
Why do tetrahedral metal complexes tend to be more intense in color?
Why do tetrahedral metal complexes tend to be more intense in color?
How is the spin selection rule partially lifted in heavier transition metals?
How is the spin selection rule partially lifted in heavier transition metals?
What must occur for a transition with ΔS ≠ 0 to happen?
What must occur for a transition with ΔS ≠ 0 to happen?
Which statement about the ΔS value in electronic transitions is correct?
Which statement about the ΔS value in electronic transitions is correct?
Which factor primarily impacts the allowedness of electronic transitions in tetrahedral complexes?
Which factor primarily impacts the allowedness of electronic transitions in tetrahedral complexes?
Which of the following orbitals is found in tetrahedral complexes that do not have 'g' symmetry?
Which of the following orbitals is found in tetrahedral complexes that do not have 'g' symmetry?
Flashcards are hidden until you start studying
Study Notes
Laporte Selection Rule
- Allowed transitions require a change in parity, indicative of a dipole moment change.
- Azimuthal quantum number (l) can change by ±1 during electronic transitions (Δl = ±1).
- Applies to transitions between gerade (g) and ungerade (u) orbitals; transitions within the same parity (g-g or u-u) are forbidden.
- Affects octahedral and square planar complexes due to their center of symmetry; but not applicable to tetrahedral complexes as they lack this symmetry.
- d→d transitions are forbidden according to Laporte's rule.
Spin Selection Rule
- States that transitions involving a change in spin multiplicity (ΔS) are forbidden; ΔS = 0 is allowed, while ΔS ≠ 0 is forbidden.
- Prohibits an electron from changing its spin state during electronic transitions, thus maintaining the integrity of spin configurations.
Relaxation of Selection Rules
- Forbidden electronic transitions can gain intensity through three mechanisms:
- Vibronic Coupling: Temporary loss of molecular symmetry during asymmetric vibrations can relax the Laporte rule.
- Mixing of States: Orbitals of different symmetry can mix, allowing transitions that were initially forbidden to occur.
- Spin-Orbit Coupling: The interaction between spin and orbital angular momentum can allow partial lifting of the spin selection rule, particularly in heavier transition metals.
Spectra of Tetrahedral Metal Ions
- Tetrahedral complexes lack a center of symmetry; thus, d-levels are represented as e and t2 without ‘g’ designations.
- This absence of symmetry enables greater intensity of color, making tetrahedral complexes more vibrant.
- Example: Cobalt(II) chloride [Co(H2O)6]2+ appears pale pink in solution, while [CoCl4]2- is intensely blue, demonstrating significant color differences.
- Cobalt blue, used historically in pottery, remains a valuable pigment for various applications today.
Spectra of Octahedral vs. Tetrahedral Complexes
- The intense d-d bands observed in tetrahedral complexes like [CoCl4]2- are contrasted with octahedral configurations like [Co(H2O)6]2+, emphasizing the strong influence of geometry on electronic transitions and overall color intensity.
Laporte Selection Rule
- Only allowed transitions involve a change in parity or a variation in the azimuthal quantum number (Δl = ±1).
- Allowed transitions: gerade (g) to ungerade (u) or vice versa.
- Transitions that maintain symmetry or are the same (g to g or u to u) are forbidden.
- Applies to octahedral and square planar complexes due to their center of symmetry; not applicable to tetrahedral complexes.
- d→d transitions are generally forbidden by the Laporte selection rule, reflecting the need for a change in dipole moment.
Spin Selection Rule
- Transitions that change spin multiplicity are forbidden; ΔS = 0 is allowed, ΔS ≠ 0 is forbidden.
- Electron spins must remain unchanged during electronic transitions.
- Example: In d5 high spin complexes, ΔS = 0 (allowed) and ΔS = 1 (forbidden).
Relaxation of Selection Rules
- Mechanisms that enable ‘forbidden’ transitions to occur include:
- Vibronic Coupling: Temporary loss of center of symmetry during unsymmetrical vibrations.
- Mixing of States: Symmetry properties of neighboring states may mix, affecting transitions.
- Spin-Orbit Coupling: Interaction between spin and orbital angular momentum allows some relaxation of spin rules.
Tetrahedral vs Octahedral Complexes
- Tetrahedral complexes lack a center of symmetry, so the Laporte rule is less restrictive, resulting in brighter colors.
- Example: [Co(H2O)6]²⁺ is pale pink, while [CoCl4]²⁻ is intense blue.
- Cobalt blue, with historical significance in pottery, increases color intensity in tetrahedral complexes.
Electronic Transition Intensities
- Classification of transition types includes:
- Spin forbidden, Laporte forbidden: e.g., [Mn(H2O)6]²⁺ shows low intensity (0.1).
- Spin allowed, Laporte forbidden: e.g., [Co(H2O)6]²⁺ shows moderate intensity (1-10).
- Spin allowed, Laporte allowed: e.g., KMnO4 shows high intensity (1000-10^6).
Charge Transfer Spectra
- Charge transfer spectra require a molecular orbital framework, involving σ and π bonding.
- Complexes can have varied absorption characteristics, especially in ultraviolet range.
Fluorescence
- Fluorescence occurs when a substance emits light post absorption of electromagnetic radiation, often with lower energy than absorbed.
- Fluorescent behavior can be observed in UV-irradiated complexes leading to visible light emission.
Crystal Field Theory (CFT)
-
Advantages:
- Explains colors and magnetic properties of metal complexes.
- Classifies ligands as strong or weak.
- Accounts for shape distortion in some complexes.
-
Disadvantages:
- Overlooks covalent bonding aspects and orbital overlap.
- Cannot predict shapes of complexes without hybridization context.
- Charge transfer spectra are inadequately explained within CFT.
Problem Solving: Color Intensity Order
- Arrange complexes by color intensity: Fe4[Fe(CN)6]3, [CoBr4]²⁻, [MnF6]⁴⁻.
- Order reasoning:
- Fe4[Fe(CN)6]3 - Spin Forbidden, Laporte Forbidden.
- [CoBr4]²⁻ - Spin Allowed, Laporte Allowed (Tetrahedral).
- [MnF6]⁴⁻ - Spin Allowed, Charge Transfer transition (high intensity).
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.