Coordination bond
A coordinate covalent bond, also known as a dative bond or coordinate bond is a kind of 2-center, 2-electron covalent bond in which the two electrons derive from the same atom. The bonding of metal ions to ligands involves this kind of interaction.
Coordinate covalent bonding is pervasive. In all metal aquo-complexes [M(H2O)n]x+, the bonding between water and the metal cation is described as a coordinate covalent bond. Metal-ligand interactions in most organometallic compounds and most coordination compounds are described similarly.
The term dipolar bond is used in organic chemistry for compounds such as amine oxides for which the electronic structure can be described in terms of the basic amine donating two electrons to an oxygen atom.
The arrow → indicates that both electrons in the bond originate from the amine moiety. In a standard covalent bond each atom contributes one electron. Therefore, an alternative description is that the amine gives away one electron to the oxygen atom, which is then used, with the remaining unpaired electron on the nitrogen atom, to form a standard covalent bond. The process of transferring the electron from nitrogen to oxygen creates formal charges, so the electronic structure may also be depicted as
This electronic structure has an electric dipole, hence the name polar bond. In reality, the atoms carry fractional charges; the more electronegative atom of the two involved in the bond will usually carry a fractional negative charge. One exception to this is carbon monoxide. In this case, the carbon atom carries the fractional negative charge although it is less electronegative than oxygen.
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