What are metal carbonyls and its classifications?, Chemistry

Metal carbonyls of transition elements constitute another important class of organometallic compounds. All d-block elements which contain only carbonyl ligands are called homoleptic carbonyls.

Amond in 1890 prepared the first homoleptic carbonyl, Ni(CO)4. Later on a large number of neutral binary carbonyl like, Fe(CO)5, Cr(CO)6, Mo(CO)6, W(CO)6 were prepared. In addition to mononuclear metal carbonyls mentioned above, transition metals from many polynuclear metal carbonyls such as Fe3(CO)12, Mn2(CO)10. The metal carbon bonds in metal carbonyls possess both σ and π character.

Classification of metal carbonyls

Metal carbonyls are classified into two types:

(i) Mononuclear (or monomeric) carbonyls: these are such compounds which contain only one metallic atom per molecule. For example, V(CO)6, Cr(CO)6, etc.

(ii) Polynuclear carbonyls: these contain two or more metallic atoms per molecule and are of the type Mx(CO)y. These carbonyls are also sometimes called as bridged carbonyls. Polynuclear carbonyls may be homonuclear e.g., Fe3(CO)12 or heteronuclear e.g.,MnCo(CO)9, MnRe(CO)10.

Nomenclature of metal carbonyls

(i) In metal carbonyls the metal atom is in zero oxidation sate therefore it may not be mentioned.

(ii) If the metal atom appears two or more times than the word di, ter etc is added before the name of metal atom.

(iii) If the CO groups act as bridge between the two metals atoms then the Greek letter mu (378_magnetic property5.png) is written before their names.

(iv) When the metal-metal bond is present between similar atoms than the multiple prefixes, bis, tris, etc. are taken.

(v) While writing the names of π bonded organometallic compounds the symbol prefixes, hapto (η) is used before the name of molecule indicating the number of carbon atoms in the carbon bonded ligand.

Some examples are given below to illustrate the above points.
Ni(CO)4 Tetracarbonylnickel
Mn2(CO)10 decacarbonyl dimanganese
Co2(CO)8 Octacarbonyl dicobalt
Fe(CO)9 Enneacarbonyldiiron
(CO)3-Co-(CO)2-Co(CO)3 Di-378_magnetic property5.png-carbonyl bis (tricarbonyl cobalt)
(CO)4Co-Co-(CO)4 Bis (tetracarbonyl cobalt)
(CO)3Fe(CO)3Fe(CO)3 Tri-378_magnetic property5.png-Carbonyl bis (tricarbonyl iron)
(C6H6) Cr(CO)3 (η6-benzene) tricarbonyl chromium    
Fe(CO3) (C4H6) (η4-butadiene) tricarbonyl iron.

Bonding in metal carbonyl

As already mentioned, the M-C bond in metal carbonyls has σ as well as π character. The metal-carbon σ bond is formed by the donation of lone pair of electrons on the carbonyl carbon into a vacant orbital of the metal. The metal-carbon π bond is formed by the donation of a pair of electrons from a filled d-orbital of metal into the vacant antibonding pi-molecular orbital (π) of carbon monoxide.

The metal to ligand bonding generates a synergic effect that reinforces the bond between CO and the metal.

Preparation of metal carbonyls

Finely divided nickel reacts with CO at room temperature to form Ni(CO)4.
Ni + 4CO  510_metal carbonyls.png  Ni(CO)4

Iron reacts with CO at higher temperature and pressure.
Fe + 5CO  510_metal carbonyls.png  Fe(CO)5

Nickel can be purified by first converting it into volatile Ni(CO)4 and subsequent thermal decomposition of Ni(CO)4. This process is known as Mond process.

Properties of metal carbonyls

1. Metal carbonyls are generally solids at room temperature and pressure. However Nickel carbonyls are liquids.

2. The mononuclear carbonyls are unstable and noxious.

3. Mononuclear carbonyls are either colourless or light coloured whereas polynuclear carbonyls are more deeply coloured. For example, Fe(CO)5 is light straw coloured liquid while Fe3(CO)12 is a deep green solid.

4. With exception of Fe2(CO)9, carbonyls are soluble in hydrocarbon solvents.





Posted Date: 6/25/2012 7:43:44 AM | Location : United States

Related Discussions:- What are metal carbonyls and its classifications?, Assignment Help, Ask Question on What are metal carbonyls and its classifications?, Get Answer, Expert's Help, What are metal carbonyls and its classifications? Discussions

Write discussion on What are metal carbonyls and its classifications?
Your posts are moderated
Related Questions
two reasons why is it necessary to ionise chromium atomsin a sample

100 mol/hr pentane flows through an adiabatic heat exchanger where it is heated isobarically (at 2.5 bar) from 50°C to 250°C. The pentane is heated by contacting pipes filled with

names of acid redicals of group 1

Chemical Properties of Ethers Ethers are fairly stable compounds. These are not simply reacted along with alkalies, dilute mineral acids, active metals, oxidising agents within

formula for producer gas

Elements of Group 13 are namely, boron, aluminium, gallium, indium and, thallium. While studying the alkali and alkaline earth metals, you have seen that all the elements of these

Saponification value - Analysis of oils and fats It is quantify of fatty acids denote as esters in oils and fats. It is described as the number of milligrams of KOH needed to s

The amount of energy released when one mole of bonds are formed among the corresponding gaseous atoms is known as Bond energy.

what is the cycle of caban dioxide and how it flow

what are the chemical poperties of p-block elements ?