A quadruple bond is a type of chemical bond between to atoms involving 8 electrons. This bond is an extension of the familiar types of bonding covalent bonds, double bonds and triple bonds To Boldly Pass the Metal-Metal Quadruple Bond Udo Radius, Frank Breher Angewandte Chemie International Edition Volume 45, Issue 19 , Pages 3006 - 3010 2006 Abstract. Quadruple bonds are rare and have been found to exist only for the transition metal elements rhenium, tungsten and chromium.

The first chemical compound, Cr₂(μ-O₂CMe)₄(H₂O)₂, containing a quadruple bond was synthesized in 1844 by E. Peligot based on a chromium quadruple bond with four acetate and two water ligands.

The archetypal quadruple bond was found in potassium octachlorodirhenate(III) or K₂^*·2H₂O by F.A. Cotton in 1964. The Rhenium - rhenium bond length in this compound is only 2.24 Angstrom.

The bonding in these compounds is described as σ²π⁴δ² with one sigma bond, two π bonds and one weak delta bond. The effective participation of the delta bond is a matter of debate. The calculated bond order for the Re₂C₈ anion is 3.2 and not 4.

A tungsten compound with a quadruple bond is di-tungsten tetra(hpp).

See also

• The Quintuple bond

References