Difference Between Coordination Compound and Organometallic Compound

Key Difference – Coordination Compound vs Organometallic Compound
 

Coordination compounds and organometallic compounds are complex compounds. The key difference between coordination compound and the organometallic compound is that coordination compounds contain coordinate covalent bonds whereas organometallic compounds contain metal-carbon bonds.

Coordination compounds are complex compounds composed of a metal ion surrounded by molecules or ions rich with electrons. These surrounding components are known as ligands. Organometallic compounds are complex compounds in which Metal-Carbon covalent bonds exist. If there is at least one metal-carbon bond, that compound is considered as an organometallic compound.

CONTENTS

1. Overview and Key Difference
2. What is Coordination Compound
3. What is Organometallic Compound
4. Relationship Between Coordination Compound and Organometallic Compound
5. Side by Side Comparison – Coordination Compound vs Organometallic Compound in Tabular Form
6. Summary

What is Coordination Compound?

Coordination compounds are complex compounds containing central metal atoms or ions surrounded by electron-rich molecules or ions known as ligands. These ligands are bonded to the metal atom (or ion) via coordinate covalent bonds. A coordinate covalent bond is formed when lone electron pairs of a ligand are donated to empty d orbitals of a metal atom or metal ion. Most of the times, transition metal atoms undergo this type of compound formation because these atoms are rich with empty d atomic orbitals.

Coordination compounds can be neutral (Co(NH₃)Cl₃), positively charged ([Nd(H₂O)₉]³) or negatively charged ([UF₈]⁴). The charged coordination compounds are also known as complex ions. Different coordination complexes have different structures known as geometries. The geometry of a coordination compound is determined by the coordination number of the complex. Coordination number is the number of ligands bonded to the central metal atom or ion.

• Coordination number = 2 is the linear geometry
• Coordination number = 3 is the trigonal planar geometry
• Coordination number = 4 is the tetrahedral or square planar geometry
• Coordination number = 5 is the trigonal bipyramidal geometry
• Coordination number = 6 is the octahedral geometry
• Coordination number = 7 is the pentagonal bipyramidal geometry
• Coordination number = 8 is the square antiprismatic geometry

What is Organometallic Compound?

Organometallic compounds are complex compounds in which Metal-Carbon covalent bonds exist. These compounds have covalent bonds between the carbon and metal atoms. However, there are some exceptions as well; metal-cyano bonds are not considered as organometallic bonds. Metal carbonyl complexes are considered as organometallic compounds.

The metal involved in the formation of organometallic chemical bond can be an alkali metal, alkaline earth metal, a transition metal or can be even a metalloid such as Boron. Some common examples for organometallic compounds are Grignard reagent containing either Lithium (Li) or Magnesium (Mg), ferrocene, tetracarbonyl nickel, etc. Boron is a metalloid, but it also forms organometallic compounds such as organoborane compounds.

Organometallic compounds are good sources of nucleophilic carbon atoms. That is because the electronegativity of the metal is very low compared to carbon. Hence, the metal atom can form a cation easily, by giving bond electrons to the carbon atom. Now, the carbon atom is rich with electrons, thus can act as a nucleophile. This carbon nucleophile can attack electrophilic carbon atoms and form new Carbon-Carbon bonds.

What is the Relationship Between Coordination Compound and Organometallic Compound?

• Some coordination compounds contain metal ions surrounded by organic ligands. If these ligands are bound to the metal atom via heteroatoms such as oxygen and nitrogen, then the compound is considered as a coordination compound. But if there are direct bonds between carbon atoms and the metal atom, then it is considered as an organometallic compound.

What is the Difference Between Coordination Compound and Organometallic Compound?

Coordination Compound vs Organometallic Compound
Coordination compounds are complex compounds containing central metal atoms or ions surrounded by electron-rich molecules or ions known as ligands.	Organometallic compounds are complex compounds in which Metal-Carbon covalent bonds exist.
Chemical Bonding
Coordination compounds contain coordinate covalent bonds between metal atoms and ligands.	Organometallic compounds contain at least one metal-carbon covalent bond.
Components
Coordination compounds contain metal atoms or ions and electron-rich ligands.	Organometallic compounds contain metal atoms and an organic portion of a molecule.
Colour
Almost all the coordination compounds are very colourful based on the oxidation state of the central metal atom.	Organometallic compounds are not essentially colourful.

Summary – Coordination Compound vs Organometallic Compound

Coordination compounds are complex compounds composed of a metal atom or a metal ion surrounded by electron-rich ligands. These ligands are bonded to the metal atom via coordinate covalent bonds. Organometallic compounds are complex compounds that have at least one Metal-Carbon bond. The difference between coordination compound and the organometallic compound is that coordination compounds contain coordinate covalent bonds whereas organometallic compounds contain metal-carbon bonds.

Reference:

1.“Coordination Compounds.” Chemistry LibreTexts, Libretexts, 19 Jan. 2018. Available here 
2.“Organometallic Chemistry.” Wikipedia, Wikimedia Foundation, 27 Mar. 2018. Available here  

Image Courtesy:

1.’Metal-EDTA’By Smokefootderivative work: Chamberlain2007 (talk) – Medta.png, (Public Domain) via Commons Wikimedia  
2.’Ferrocene-2D’By The original uploader was Benjah-bmm27 at English Wikipedia (Public Domain) via Commons Wikimedia