Question

Complex X of composition $Cr(H_2O)_6Cl_n$ has a spin only magnetic moment of 3.83 BM. It reacts with $AgNO_3$ and shows geometrical isomerism. The IUPAC nomenclature of X is :

• A. Tetraaquadichlorido chromium(IV) chloride dihydrate
• B. Hexaaqua chromium(III) chloride
• C. Dichloridotetraaqua chromium(IV) chloride dihydrate
• D. Tetraaquadichlorido chromium(III) chloride dihydrate

Answer 1

The Correct Option is D

To determine the IUPAC name of the complex $Cr(H_2O)_6Cl_n$, we need to consider the given information:

1. The complex has a spin-only magnetic moment of 3.83 BM (Bohr Magneton).
2. It reacts with $AgNO_3$ and shows geometrical isomerism.
3. The complex is of the type $Cr(H_2O)_6Cl_n$.

Let us analyze each piece of information step by step:

Analyzing the Spin-Only Magnetic Moment

The spin-only magnetic moment is given by the formula:

\[\mu = \sqrt{n(n+2)}\]

where n is the number of unpaired electrons. Given that the magnetic moment is 3.83 BM, we can solve for n:

\[\sqrt{n(n+2)} = 3.83\]

Upon solving, n approximately equals 3. This indicates there are 3 unpaired electrons.

Determining the Coordination and Oxidation State

The presence of 3 unpaired electrons suggests that it is a d^3 configuration. In the case of chromium, this configuration stems from the oxidation state +3 (as Cr^{3+}). Given the hint of geometrical isomerism and the magnetic data, the probable form of the complex is [Cr(H_2O)_4Cl_2]Cl\cdot2H_2O.

Reactivity with AgNO₃ and Geometrical Isomerism

The complex will react with $AgNO_3$ to precipitate 1 mole of $AgCl$, indicating the presence of one chloride ion outside the coordination sphere. Also, the complex must be cis if it shows geometrical isomerism, which is only possible if it is octahedral.

Conclusion and IUPAC Naming

The given information correctly aligns with the option:

Tetraaquadichlorido chromium(III) chloride dihydrate

This name indicates:

• Tetraaqua: four water molecules are coordinated to chromium.
• Dichlorido: two chloride ions are coordinated.
• chromium(III): Chromium is in the +3 oxidation state.
• chloride: one uncoordinated chloride ion in the formula.
• dihydrate: two water molecules are outside the coordination sphere in the crystal lattice.