Question

The sum of coordination number and oxidation number of the metal M in the complex \[ [M({en})_2(C_2O_4)] \quad {(en = ethylenediamine)} \]

• A. 8
• B. 6
• C. 7
• D. 9

Hint:

1. Coordination Number: Count the number of donor atoms from the ligands that bond with the metal. Both 'en' and 'C₂O₄²⁻' are bidentate. 
2. Oxidation Number: Use the charge balance method. Set the total charge of the complex equal to zero, considering the charges of the ligands.

Answer 1

The Correct Option is D

To find the sum of the coordination number and the oxidation number of the metal M in the complex \( [M(en)_2(C_2O_4)] \), we need to determine each value separately.

1. Coordination Number:

The coordination number is the number of ligands directly attached to the central metal ion through coordinate bonds. In this complex:

• en (ethylenediamine): It is a bidentate ligand, meaning it coordinates to the metal ion through two donor atoms (nitrogen atoms). In the complex, there are two 'en' ligands. Thus, the contribution to the coordination number from 'en' ligands is \( 2 \times 2 = 4 \).
• C\(_2\)O\(_4^{2-}\) (oxalate): It is also a bidentate ligand, coordinating through two oxygen atoms. In the complex, there is one 'C\(_2\)O\(_4^{2-}\)' ligand. Thus, the contribution to the coordination number from the 'C\(_2\)O\(_4^{2-}\)' ligand is \( 1 \times 2 = 2 \).

The total coordination number of the metal M is the sum of contributions from all ligands:

    Coordination Number = (Contribution from 2 'en' ligands) + (Contribution from 1 'C2O42- ligand)
    = 4 + 2 = 6
    

2. Oxidation Number:

To find the oxidation number of metal M, we consider the charge of the complex and the charges of the ligands. The complex \( [M(en)_2(C_2O_4)] \) is neutral as there is no overall charge indicated.

• en (ethylenediamine): It is a neutral ligand, so its charge is 0.
• C\(_2\)O\(_4^{2-}\) (oxalate): It has a charge of -2.

Let the oxidation number of metal M be \(x\). The sum of the oxidation numbers of all components in a neutral complex must be zero:

    Oxidation Number of M + 2 * (Charge of 'en') + 1 * (Charge of 'C2O42-) = 0
    x + 2 * (0) + 1 * (-2) = 0
    x - 2 = 0
    x = +2
    

Thus, the oxidation number of the metal M is +2.