Question

What are the value of m and n in the anionic species \[{\left[ {V{{\left( {CO} \right)}_m}} \right]^{n - }}\], if it is following Sidgwick E.A.N rule and having octahedral shape?
A. \[m = 4,n = 1\]
B. \[m = 6,n = 2\]
C. \[m = 6,n = 1\]
D. None of these

Answer 1

Hint: The E.A.N expresses the effective atomic number of a complex. And it indicates the total number of electrons present around the nucleus of a metal atom in a metal complex. And it is a collection of the electrons present in the metal atoms and the bonding electrons from the molecules and electrons surrounding atoms. Hence, the effective atomic number can be found by adding the atomic number of elements with the total number of electrons donated by the ligand.

Complete answer:
The number of m and not equal to four. Hence, the option (A) is incorrect.
The value n is not equal to two. Hence, the option (B) is incorrect.
Here, the given complex, \[{\left[ {V{{\left( {CO} \right)}_m}} \right]^{n - }}\] have an octahedral shape. Hence, the number of ligands connected with the vanadium metal is equal to six. Which means, m is equal to six.
And, EAN\[ = \] atomic number of metal \[ \times \]total number of electrons donated by the ligand
Here, the atomic number of vanadium is equal to \[23\]
Hence,
$EAN = 23 + n + \left( {2 \times 6} \right)$
$ = 23 + n + 12$
$35 + n$
$ \Rightarrow n = 1$
Therefore, the complex is \[{\left[ {V{{\left( {CO} \right)}_6}} \right]^ - }\]. Hence, the option (C) is correct.
The value of m and n is equal to six and one respectively. Hence, the option (D) is incorrect.

So, the correct answer is “Option C”.

Note:
 In the case of octahedral complexes, six ligands or six groups or atoms are symmetrically arranged in the central atom. The complex can exist as isomers, if two or more types of ligands are attached with the octahedral metal. The effective atomic number rule states that, in a number of metal complexes the metal has the tendency to surround itself with enough ligands that the resulting E.A.N is numerically the same as the atomic number of noble gas elements.