Question

The IUPAC name of $Fe{\left( {CO} \right)_5}$ is?
A) Pentacarbonyl ferrate (0)
B) Pentacarbonyl ferrate (II)
C) Pentacarbonyl iron (0)
D) Pentacarbonyl iron (II)

Answer 1

We need to know that a complex is a substance in which a metal atom or ion is associated with a group of neutral molecules or anions called ligands. Coordination compounds are neutral substances (i.e. uncharged) in which at least one ion is present as a complex.

Complete answer:
We have to remember that iron pentacarbonyl, also known as iron carbonyl, is the compound with formula $Fe{\left( {CO} \right)_5}$. Under standard conditions $Fe{\left( {CO} \right)_5}$ is a free-flowing, straw-colored liquid with a pungent odor. Older samples appear darker. This compound is a common precursor to diverse iron compounds, including many that are useful in small scale organic synthesis. Most metal carbonyls have $18$ valence electrons, and $Fe{\left( {CO} \right)_5}$ fits this pattern with 8 valence electrons on $Fe$ and five pairs of electrons provided by the $CO$ ligands. Reflecting its symmetrical structure and charge neutrality, $Fe{\left( {CO} \right)_5}$ is volatile; it is one of the most frequently encountered liquid metal complexes. $Fe{\left( {CO} \right)_5}$adopts a trigonal bipyramidal structure with the Fe atom surrounded by five $CO$ ligands: three in equatorial positions and two axially bound. The $Fe - C - O$ linkages are each linear. Iron is dsp3 hybridized in this complex. Most metal carbonyls can be halogenated. Thus, treatment of $Fe{\left( {CO} \right)_5}$ with halogens gives the ferrous halides $Fe{\left( {CO} \right)_4}{X_2}\;$ for $X = I,Br,Cl$. These species, upon heating, lose $CO$ to give the ferrous halides, such as iron (II) chloride. Oxidation number of iron in this complex is five.

Therefore, the option C is correct.

Note:
We need to know that upon UV irradiation $Fe{\left( {CO} \right)_5}$ absorbs light population and metal-to-CO charge transfer band inducing $CO$ photolysis and generating singlet and triplet coordinatively unsaturated intermediate $Fe{\left( {CO} \right)_4}$ with high quantum yield. Prolonged irradiation in the gas phase may proceed to further $CO$ detach until atomic Fe formation.