Class 12 Chemistry Coordination Compounds Organo-metallic compounds

Organo-metallic compounds

They are those compounds in which metal or metalloid or a non-metal is directly linked to carbon atom of a hydrocarbon.

For example: (C2H5)2Zn etc

Please note that metal cyanides and metal carbides are not organometallic compounds as in them carbon atom is not directly joined to metal.

Types of organometallic compounds:

  • Sigma organometallic compounds
  • Pi organometallic compounds

Sigma and pi organometallic compounds In detail:

  • Sigma organo-metallic compounds: these are the compounds obtained by bonding of non-metal with metalloid elements with carbon. forexample:RMgX, (CH3)3Al etc.
  • Pi organo- metalliccompound: these compounds are formed mainly by transition elements. Normal sigma bond is formed through the pi electron cloud of organic molecule. Forexample : ferrocene ,zeisse’s salt etc
  • Sigma and pi organo-metaliccompound: these compounds are formed by transition metal carbonyls .for example : Ni(CO)4,Fe(CO)5 etc

Shapes of these structures are shown below:

For example :

  1. Shape of [Ni(Co)4]



 Shape of [Fe(Co)5]



Considering bonding in metal carbonyls: these compounds possess both s and p characters. The M-C sigma bond is formed by donation of lone pair if electrons on the carbonyl carbon into a vacant orbital of metal. The M-C pi bond is formed by the donation of pair of electrons from the filled d orbital of metal into vacant antibonding pi orbital of carbon monoxide. The metal to ligand bonding creates a synergic effect which strengthens the bond between CO and metal as shown below:-



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