Delta bond

Formation of a δでるた bond by the overlap of two d orbitals

3D model of a boundary surface of a δでるた bond in Mo₂

In chemistry, a delta bond (δでるた bond) is a covalent chemical bond, in which four lobes of an atomic orbital on one atom overlap four lobes of an atomic orbital on another atom. This overlap leads to the formation of a bonding molecular orbital with two nodal planes which contain the internuclear axis and go through both atoms.^[1]^[2]^[3]^[4]

The Greek letter δでるた in their name refers to d orbitals, since the orbital symmetry of the δでるた bond is the same as that of the usual (4-lobed) type of d orbital when seen down the bond axis. This type of bonding is observed in atoms that have occupied d orbitals with low enough energy to participate in covalent bonding, for example, in organometallic species of transition metals. Some rhenium, molybdenum, technetium, and chromium compounds contain a quadruple bond, consisting of one σしぐま bond, two πぱい bonds and one δでるた bond.

The orbital symmetry of the δでるた bonding orbital is different from that of a πぱい antibonding orbital, which has one nodal plane containing the internuclear axis and a second nodal plane perpendicular to this axis between the atoms.

The δでるた notation was introduced by Robert Mulliken in 1931.^[5]^[6] The first compound identified as having a δでるた bond was potassium octachlorodirhenate(III). In 1965, F. A. Cotton reported that there was δでるた-bonding as part of the rhenium–rhenium quadruple bond in the [Re₂Cl₈]²⁻ ion.^[7] Another example of a δでるた bond is proposed in cyclobutadieneiron tricarbonyl between an iron d orbital and the four p orbitals of the attached cyclobutadiene molecule.

References

^ Cotton, F. A.; Wilkinson, G. (1988). Advanced Inorganic Chemistry (5th ed.). John Wiley. pp. 1087–1091. ISBN 0-471-84997-9.
^ Douglas, B.; McDaniel, D. H.; Alexander, J. J. (1983). Concepts and Models of Inorganic Chemistry (2nd ed.). Wiley. p. 137. ISBN 9780471895053.
^ Huheey, J. E. (1983). Inorganic Chemistry (3rd ed.). Harper and Row. pp. 743–744. ISBN 9780060429874.
^ Miessler, G. L.; Tarr, D. A. (1998). Inorganic Chemistry (2nd ed.). Prentice-Hall. pp. 123–124. ISBN 978-0138418915.
^ Jensen, William B. (2013). "The Origin of the Sigma, Pi, Delta Notation for Chemical Bonds". J. Chem. Educ. 90 (6): 802–803. Bibcode:2013JChEd..90..802J. doi:10.1021/ed200298h.
^ Mulliken, Robert S. (1931). "Bonding Power of Electrons and Theory of Valence". Chem. Rev. 9 (3): 347–388. doi:10.1021/cr60034a001.
^ Cotton, F. A. (1965). "Metal–Metal Bonding in [Re₂X₈]²⁻ Ions and Other Metal Atom Clusters". Inorg. Chem. 4 (3): 334–336. doi:10.1021/ic50025a016.

[1] Cotton, F. A.; Wilkinson, G. (1988). Advanced Inorganic Chemistry (5th ed.). John Wiley. pp. 1087–1091. ISBN 0-471-84997-9.

[2] Douglas, B.; McDaniel, D. H.; Alexander, J. J. (1983). Concepts and Models of Inorganic Chemistry (2nd ed.). Wiley. p. 137. ISBN 9780471895053.

[3] Huheey, J. E. (1983). Inorganic Chemistry (3rd ed.). Harper and Row. pp. 743–744. ISBN 9780060429874.

[4] Miessler, G. L.; Tarr, D. A. (1998). Inorganic Chemistry (2nd ed.). Prentice-Hall. pp. 123–124. ISBN 978-0138418915.

[5] Jensen, William B. (2013). "The Origin of the Sigma, Pi, Delta Notation for Chemical Bonds". J. Chem. Educ. 90 (6): 802–803. Bibcode:2013JChEd..90..802J. doi:10.1021/ed200298h.

[6] Mulliken, Robert S. (1931). "Bonding Power of Electrons and Theory of Valence". Chem. Rev. 9 (3): 347–388. doi:10.1021/cr60034a001.

[7] Cotton, F. A. (1965). "Metal–Metal Bonding in [Re₂X₈]²⁻ Ions and Other Metal Atom Clusters". Inorg. Chem. 4 (3): 334–336. doi:10.1021/ic50025a016.

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