Quintuple bond

[1][2] The chromium–chromium quintuple bond has been analyzed with multireference ab initio and DFT methods,[3] which were also used to elucidate the role of the terphenyl ligand, in which the flanking aryls were shown to interact very weakly with the chromium atoms, causing only a small weakening of the quintuple bond.

[5] In 2005, a quintuple bond was postulated to exist in the hypothetical uranium molecule U2 based on computational chemistry.

[10] Synthesis of quintuple bonds is usually achieved through reduction of a dimetal species using potassium graphite.

[citation needed] Quintuple bond lengths are heavily dependent on the ligands bound to the metal centers.

The bidentate ligand can act as a sort of tweezer in that in order for chelation to occur the metal atoms must move closer together, thereby shortening the quintuple bond length.

The two ways in which to obtain shorter metal–metal distances is to either reduce the distance between the chelating atoms in the ligand by changing the structure, or by using steric effects to force a conformational change in the ligand that bends the molecule in a way that forces the chelating atoms closer together.

However, when the hydrogen is replaced with a much more bulky phenyl ring the steric repulsion increases dramatically and the ligand "bows" which causes a change in the orientation of the lone pairs of electrons on the nitrogen atoms.

[13][14] Quintuple-bonded dichromium complexes appear to act like magnesium to produce Grignard reagents.