MChem Master of Chemistry Master of Chemistry: Inorganic Chemistry 2 ā Questions and Answers
Question 1: Which of the following best describes the trans influence in square planar complexes?
- The kinetic labilization of ligands cis to a strong trans-influencing ligand
- The thermodynamic weakening of the bond trans to a strong trans-influencing ligand (Correct answer)
- The preference of strong-field ligands to occupy axial positions
- The tendency of Ļ-acceptor ligands to stabilize the trans configuration
Correct answer: The thermodynamic weakening of the bond trans to a strong trans-influencing ligand
The trans influence is a ground-state (thermodynamic) effect whereby a strongly trans-influencing ligand weakens and lengthens the metalāligand bond trans to itself.
Question 2: In the ZieglerāNatta polymerization mechanism, the role of the titanium center is best described as:
- A BrĆønsted acid that protonates the monomer
- A Lewis acid that coordinates and inserts the olefin via a CosseeāArlman mechanism (Correct answer)
- A radical initiator that generates alkyl radicals
- A photocatalyst that promotes [2+2] cycloaddition
Correct answer: A Lewis acid that coordinates and inserts the olefin via a CosseeāArlman mechanism
Titanium acts as a Lewis acidic metal center where the alkene coordinates and inserts into the TiāC bond via the CosseeāArlman migratory insertion pathway.
Question 3: Which crystal field parameter (Ī) ordering correctly reflects the spectrochemical series for the following ligands?
- Iā» > Clā» > NHā > CNā»
- CNā» > NHā > Clā» > Iā» (Correct answer)
- NHā > CNā» > Iā» > Clā»
- Clā» > Iā» > CNā» > NHā
Correct answer: CNā» > NHā > Clā» > Iā»
The spectrochemical series ranks ligands by field strength: CNā» (strong Ļ-acceptor) > NHā (Ļ-donor) > Clā» > Iā» (weak-field halides).
Question 4: The WadeāMingosāLauher rules predict that a nido borane cluster has how many skeletal electron pairs relative to the number of vertices?
- n+1 pairs for n vertices
- n+2 pairs for n vertices (Correct answer)
- n+3 pairs for n vertices
- n pairs for n vertices
Correct answer: n+2 pairs for n vertices
Nido clusters follow the n+2 rule, meaning they have one more skeletal electron pair than a closo cluster of the same vertex count.
Question 5: Which technique is most diagnostic for distinguishing terminal, bridging, and face-capping carbonyl ligands in metal carbonyl clusters?
- UV-Vis spectroscopy
- Ā¹H NMR spectroscopy
- IR spectroscopy (Ī½(CO) stretching frequencies) (Correct answer)
- Mass spectrometry
Correct answer: IR spectroscopy (Ī½(CO) stretching frequencies)
IR spectroscopy directly measures Ī½(CO) frequencies: terminal CO (~2000 cmā»Ā¹), bridging CO (~1800 cmā»Ā¹), and face-capping CO appear at progressively lower wavenumbers.
Question 6: In the Latimer diagram for manganese in acidic solution, the MnOāā»/MnĀ²āŗ couple has EĀ° = +1.51 V. This value indicates that MnOāā» is:
- A mild reducing agent in acidic solution
- A strong oxidizing agent in acidic solution (Correct answer)
- Thermodynamically stable against disproportionation in acid
- A weaker oxidant than CrāOāĀ²ā» in acid
Correct answer: A strong oxidizing agent in acidic solution
A large positive standard reduction potential indicates permanganate is a powerful oxidizing agent that readily accepts electrons in acidic media.
Question 7: Prussian blue, Feā[Fe(CN)ā]ā, exhibits intense color due to which phenomenon?
- d-d electronic transitions forbidden by the Laporte rule
- Intervalence charge transfer (IVCT) between FeĀ²āŗ and FeĀ³āŗ centers (Correct answer)
- Ligand-to-metal charge transfer (LMCT) from CNā» to iron
- Metal-to-ligand charge transfer (MLCT) from iron to CNā» Ļ*
Correct answer: Intervalence charge transfer (IVCT) between FeĀ²āŗ and FeĀ³āŗ centers
Prussian blue's deep blue color arises from intervalence charge transfer where an electron moves between FeĀ²āŗ (low-spin, C-bound) and FeĀ³āŗ (high-spin, N-bound) sites.
MChem Master of Chemistry Master of Chemistry: Inorganic Chemistry 2
Which of the following best describes the trans influence in square planar complexes?