Exams › JEE Advanced › Chemistry

Which of the following metal carbonyl complexes satisfy BOTH conditions: (i) C-O bond length greater than in Fe(CO)5, and (ii) obey the 18-electron rule?

1. [Mn(CO)5]⁻
2. [Fe(CO)4]²-
3. [CuCl(CO)(H2O)2]
4. [Cr(CO)6]

Correct answer: [Mn(CO)5]⁻

Solution

[Mn(CO)5]⁻ has Mn(-I), making it more electron-rich than Fe(0) in Fe(CO)5, so greater pi back-donation elongates the C-O bond; it also has 18 electrons. [Fe(CO)4]²- has Fe(-II), even more electron-rich, and is also 18e. Both A and B satisfy both conditions.

Related JEE Advanced Chemistry questions

• The pair(s) of coordination complexes/ions exhibiting the same kind of isomerism is(are) -
• A 0.01 molal solution of a cobalt(III) chloride-ammonia complex, which dissociates completely, has a freezing point of -0.0558°C. Based on this data, how many chloride ions are present within the coordination sphere of the complex? [Kf for water = 1.86 K kg mol⁻¹]
• What are the molecular shapes of the ammonia complexes formed by Ni²⁺, Pt²⁺, and Zn²⁺, respectively?
• What are the spin-only magnetic moments (in Bohr Magneton) for the complexes [Cr(NH₃)₆]³⁺ and [CuF₆]³⁻, given that the atomic numbers of Cr and Cu are 24 and 29, respectively?
• When K3[Fe(CN)6] reacts with freshly prepared FeSO4, a dark blue solid known as Turnbull's blue is formed. On the other hand, when K4[Fe(CN)6] reacts with FeSO4 in the complete absence of air, a white solid X is produced, which later turns blue when exposed to air. Additionally, if FeSO4 is mixed with NaNO3 and concentrated H2SO4 is carefully added along the side of a test tube, a brown ring forms. What is the chemical identity of precipitate X?
• Which of the following compounds is responsible for the appearance of the brown ring?

⚔️ Practice JEE Advanced Chemistry free + battle 1v1 →