Special Cases
Pi bonds do not necessarily connect a pair of atoms that are also sigma-bonded.
In certain metal complexes, pi interactions between a metal atom and alkyne and alkene pi antibonding orbitals form pi-bonds.
In some cases of multiple bonds between two atoms, there is no sigma bond at all, only pi bonds. Examples include diiron hexacarbonyl (Fe2(CO)6), dicarbon (C2), and the borane B2H2. In these compounds the central bond consists only of pi bonding, and in order to achieve maximum orbital overlap the bond distances are much shorter than expected.
Read more about this topic: Pi Bond
Famous quotes containing the words special and/or cases:
“Passengers in 1937 totaled 270,000; so many of these were celebrities that two Newark newspapers ran special airport columns.”
—For the State of New Jersey, U.S. public relief program (1935-1943)
“Colonel, never go out to meet trouble. If you will just sit still, nine cases out of ten someone will intercept it before it reaches you.”
—Calvin Coolidge (1872–1933)