The key difference between back bonding and coordinate bonding is that back bonding refers to a chemical bond that forms between an atomic orbital of one atom and an antibonding orbital of a ligand whereas coordinate bonding refers to the sharing of a pair of electrons between an electronegative species and an electro-deficient species.
Coordinate bonds commonly occur in coordination complexes in which a central metal atom is surrounded by a set of ligands, which are bonded to the metal atom through coordinate bonds. Here, the ligands share their lone electron pairs with the metal atom. But, in back bonding, a chemical bond forms between an atomic orbital of one atom and an antibonding orbital of another atom when they have equivalent symmetries. In organometallic chemistry, this type of chemical bonds is common.
CONTENTS
1. Overview and Key Difference
2. What is Back Bonding
3. What is Coordinate Bonding
4. Side by Side Comparison – Back Bonding vs Coordinate Bonding in Tabular Form
5. Summary
What is Back Bonding?
Back bonding or pi-back bonding is a situation where electrons of an atomic orbital of one atom move to an antibonding orbital of another atom, forming a chemical bond. Here, the two forms of orbitals should have appropriate symmetry. Usually, the atom with the atomic orbital is a transition metal while the atom with the antibonding orbital is a part of a pi-acceptor ligand. In organometallic chemistry, this type of chemical bond is common, and it has transition metals complexed with multiatomic ligands, e.g., carbon monoxide, ethylene, nitrosonium ion.
Figure 01: Back Donation
Moreover, back bonding is a synergic process. It involves the donation of electrons from an orbital which is filled with electrons or containing a lone electron pair into an empty orbital of the transition metal, together with the release of electrons from a d orbital of the metal into an antibonding orbital of the ligand.
What is Coordinate Bonding?
Coordinate bonding refers to a covalent bond in which the shared bond electrons are provided by one of the two atoms in the bond. That means; one atom donates one of its lone electron pairs to another atom, and the lone electron pair is shared between the two atoms thereafter. Since it is a donation, we can name it as a dative bond or dipolar bond as well.
Figure 02: A Dative Bond Formation Process
When drawing the chemical structures, we can show the coordinate bond using an arrow; the arrowhead shows which atom accepted electrons and the arrow tail starts from the atom that donated the electron pair. However, it is also a type of covalent bond; therefore, we replace this arrow with a usual line to show that it is a bond where an electron pair is shared. These bonds are commonly found in coordination complexes where a metal ion accepts lone electron pairs from ligands.
What is the Difference Between Back Bonding and Coordinate Bonding?
Back bonding and coordinate bonding are two different covalent bonds. The key difference between back bonding and coordinate bonding is that back bonding refers to the chemical bond that forms between an atomic orbital of one atom and an antibonding orbital of a ligand whereas coordinate bonding refers to the sharing of a pair of electrons between an electronegative species and an electro-deficient species.
Below infographic briefs the difference between back bonding and coordinate bonding.
Summary – Back Bonding vs Coordinate Bonding
Back bonding and coordinate bonding are two different forms of covalent bonds. The key difference between back bonding and coordinate bonding is that back bonding refers to the chemical bond that forms between an atomic orbital of one atom and an antibonding orbital of a ligand whereas coordinate bonding refers to the sharing of a pair of electrons between an electronegative species and an electro-deficient species.
Reference:
1. Helmenstine, Anne Marie. “Dative Bond Definition (Coordinate Bond).” ThoughtCo, Oct. 14, 2019, Available here.
Image Courtesy:
1. “Back bonding” By OMCV – Own work (Public Domain) via Commons Wikimedia
2. “NH3-BF3-adduct-bond-lengthening-2D” By Ben Mills – Own work (Public Domain) via Commons Wikimedia
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