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September 26, 2005
Volume 83, Number 39
p. 9

MULTIPLE BONDING

'Quintuple' Bond Makes Its Debut

First stable molecule with fivefold metal-metal bonding is synthesized

Steve Ritter

COURTESY OF DAVID BAKER

HIGH FIVE Quintuple bond is proposed to form by the sharing of five electron pairs in five bonding 3d orbitals in this chromium dimer with bulky terphenyl ligands (R = isopropyl).

F. Albert Cotton and his coworkers at Texas A&M University surprised chemists in 1964 with evidence that the [Re2Cl8] ion contained the first known multiple bond between two metal atoms. Not only was it a multiple bond, it was an unprecedented quadruple bond. Cotton convinced the world that he was right, and inorganic chemistry hasn't been the same since.

Now, Philip P. Power at the University of California, Davis, and his coworkers report evidence for the first "quintuple" bond between two metal atoms in the dichromium complex, RCrCrR, where R is a bulky terphenyl ligand (Science, published online Sept. 22, dx.doi.org/10.1126/science.1116789). The chromium dimer exists as air- and moisture-sensitive dark red crystals that are stable up to