Quiz: Transition Metal Complexes and Bonding — 10 perguntas

1. In a transition metal complex, what best describes the bonding interaction between the metal centre and the ligand?

A. A Lewis acid metal centre accepts electron density from a Lewis base ligand

B. A ligand donates protons to a metal centre through ionic attraction

C. Two neutral species share electrons equally in a covalent bond

D. A Lewis base metal centre donates electron density to a Lewis acid ligand

Answer: (A)

Explicação

A transition metal complex is described as a coordinate interaction in which the metal acts as a Lewis acid and the ligand acts as a Lewis base. The ligand donates electron density to the metal to form the bond.

2. What is a transition metal complex?

A. A bonding interaction between a Lewis acid metal center and a Lewis base ligand.

B. A compound formed solely by ionic bonds between metals and nonmetals.

C. A structure where transition metals are bonded exclusively through covalent bonds.

D. A molecule where a transition metal is bonded to only one ligand.

Answer: (A)

Explicação

A transition metal complex is defined as a bonding interaction between a Lewis acid metal center and a Lewis base ligand, involving coordinate covalent bonds.

3. Which set of descriptors is used to characterise a transition metal complex?

A. Ligand pKa, bond length, hybridisation, and boiling point

B. Formal oxidation state, d electron count, coordination number/shape, and magnetic moment

C. Molecular mass, colour, density, and melting point

D. Charge, polarity, solubility, and electronegativity

Answer: (B)

Explicação

The key descriptors listed are the formal oxidation state, d electron count, coordination number or shape, and magnetic moment. These are the standard features used to characterise the complex in this material.

4. What is the primary purpose of the spectrochemical series in coordination chemistry?

A. To determine the stability of different metal-ligand bonds.

B. To predict the magnetic properties of transition metal complexes.

C. To rank ligands based on their ability to produce ligand field splitting in a metal complex.

D. To classify ligands according to their charge and size.

Answer: (C)

Explicação

The spectrochemical series ranks ligands by the strength of the ligand field splitting they induce, which influences the electronic and optical properties of the complex.

5. What does the spectrochemical series rank?

A. Complexes by the number of coordinated ligands they contain

B. Orbitals by their radial size in an isolated atom

C. Ligands by the strength of the ligand field splitting they produce on a metal

D. Metals by their oxidation state in increasing order

Answer: (C)

Explicação

The spectrochemical series orders ligands according to how strongly they split the metal d orbitals. In the given order, weak-field ligands such as I− appear first and strong-field ligands such as CO appear last.

6. When was the concept of octahedral sigma-donor complexes first systematically described in the literature?

A. During the development of crystal field theory in the 1930s

B. In the early 20th century, around 1910-1920

C. In the 1950s with the advent of molecular orbital theory

D. In the 1980s with advanced spectroscopic techniques

Answer: (A)

Explicação

The systematic description of octahedral sigma-donor complexes was developed during the 1930s as part of the broader development of crystal field theory, which explained ligand field splitting and bonding in transition metal complexes.

7. How does crystal field theory explain bonding in a complex?

A. By replacing ligand effects with direct metal–metal bonding

B. By assuming all metal–ligand bonds are purely ionic and unsplit

C. By focusing only on proton transfer between ligand and metal

D. By treating the metal d orbitals as split by the surrounding ligand field

Answer: (D)

Explicação

Crystal field theory explains complex bonding by describing how the ligand field splits the metal d orbitals into different energy levels. It does not rely on proton transfer or metal–metal bonding for this explanation.

8. How does ligand field splitting energy (Δo) in an octahedral complex differ from the eg–t2g energy gap, and why is this distinction important?

A. Δo describes the energy difference caused by ligand interactions, whereas eg–t2g is a measure of the overall ligand field strength; confusing them leads to incorrect electron counting.

B. Δo measures the energy difference between t2g and eg* orbitals, whereas eg–t2g refers to the splitting within the d orbitals; this distinction is crucial for understanding electron occupancy and stability.

C. Δo is the energy difference between the highest and lowest d orbitals, while eg–t2g is the splitting within the eg set; the distinction is mainly academic and has little practical impact.

D. Δo is the energy gap between bonding and antibonding orbitals, while eg–t2g is the energy difference between ligand and metal orbitals; the distinction affects ligand strength.

Answer: (B)

Explicação

Δo specifically refers to the energy gap between the t2g and eg* orbitals in an octahedral field, which is used to assess ligand field strength. The eg–t2g gap is a common misconception; the correct Δo involves the non-bonding t2g and antibonding eg* orbitals, which is essential for understanding electron occupancy and stability.

9. Who is credited with proposing the 18-electron rule that predicts stability in transition metal complexes?

A. Robert H. Grubbs

B. Gilbert Lewis

C. Linus Pauling

D. Niels Bohr

Answer: (B)

Explicação

Gilbert Lewis is credited with proposing the 18-electron rule, which predicts the stability of certain transition metal complexes based on electron count.

10. What is the primary consequence of applying the 18-electron rule to transition metal complexes, particularly in relation to their stability and geometry?

A. It indicates that complexes with fewer than 18 electrons are always unstable and tend to decompose.

B. It predicts that complexes with 18 electrons are generally more stable and often adopt specific geometries such as octahedral or square planar.

C. It implies that the electron count has no significant effect on the stability or geometry of the complex.

D. It suggests that complexes with more than 18 electrons are more stable due to increased electron-electron repulsion.

Answer: (B)

Explicação

The 18-electron rule predicts that transition metal complexes with a total of 18 valence electrons tend to be particularly stable and often adopt geometries like octahedral or square planar, which maximize electron pairing and orbital filling.