Question

For the complex $\left[ {Fe{{\left( {CO} \right)}_x}} \right]$ . What is wrong?
$A.$ It is $\sigma - \pi$ bonded organometallic compound
$B.$ In the complex value of $x = 6$
$C.$ In the complex $CO$ is $\pi$ acid ligand.
$D.$ It is trigonal bipyramidal shape.

Answer 1

$\left[ {Fe{{\left( {CO} \right)}_x}} \right]$ is a coordination compound in which central atom is Ion and $CO$ is acts as ligand (ligand is a molecule or an ion, which can donate the electron pair to the central atom or ion to form coordination complex). Ligand can be anions, cations and neutral. It acts as Lewis base as they donate electron pairs.

Complete answer:
In the given question we have checked all of them one by one what is wrong in the question.
First option is correct it is $\sigma - \pi$ bonded organometallic compound it donates its sigma to an empty $d -$ orbital of the metal which is iron is this case and the filled $d -$ orbital of $Fe$ atom donates to the empty $\pi -$ orbital of $CO$ . In the compound when a metal is bonded with a carbon atom. The compound is known as an organometallic compound.
Second statement is wrong in that it is in the complex value of $x = 6$ . The value of can be calculated by using formula
$EAN = Z - x \times n + O.S$
Where $EAN$ is the effective atomic number ($36$ in this case), $Z$ is the atomic number of central atom, $x$ is number of ligand attach, $n$ is the number of electron donated by each ligand and $O.S$ is the positive oxidation state of metal. By using above formula, we get the value of x
$36 = 26 - 2x + 0$
$= 5$
So, the statement is wrong
Third statement is true $CO$ is $\pi -$ acid ligand. $CO$ is a good $\pi -$ acceptor due to empty $\pi -$ orbital and a good sigma donor. When ligand is bonding to a metal (ligand is $CO$ in this case ). Sigma donates to an empty $d -$ orbital of the central metal ($Fe$ in this case). And the filled $d -$ orbital of the metal donates to the empty $\pi -$ orbital of $CO$ . Hence $CO$ is $\pi -$ acid ligand.
Fourth statement is also true; it has the trigonal bipyramidal shape with the $Fe$ atom surrounded by five $CO$ ligand .Three in equatorial position and the remaining two at axial position. It has five bond pairs, According to the $VSEPR$ theory it possesses trigonal bipyramidal shape.

Thus the option $\left( B \right)$ is correct.

Note:
Coordination compounds are neutral substances in which at least one ion is present as a complex. $\left[ {Fe{{\left( {CO} \right)}_x}} \right]$ is a complex coordination compound in which the central atom is iron and its coordination number is 5. Coordination number is defined as the total number of ligands attached to it.