# Are there any molecules with delta bonds in their ground states?

When looking at excited states of molecules, $\delta$ bonds are relatively common, but I've never come across a molecule with a $\delta$ bond in its ground state.

Are there molecules with $\delta$ bonds in their ground states?

What about even higher angular momentum states ($\phi$ and $\gamma$ bonds)?

Chromium(II) acetate has a Cr-Cr quadruple bond - and hence a $\delta$ bond - in its ground state. This sort of "paddlewheel" configuration, with four carboxylic acids coordinating a pair of metal ions, is reasonably common (see also copper(II) acetate, for instance), although the extent to which the metals can be considered covalently bonded varies.

• The copper analog is another example – khaverim Mar 3 '16 at 13:15

Metal-metal quadruple bonds have seemingly been reported for several cases, quite often by F. A. Cotton. A short search revealed a more recent report on a species with a Cr-Cr quintuple bond: Synthesis of a Stable Compound with Fivefold Bonding Between Two Chromium(I) Centers.

According to Gagliardi and Roos, there should be a φ bond in the ground state of the $\ce{U2}$ molecule. That being said, it is probably incredibly tough to synthesise this molecule.
• I figure you could make $\ce{U2}$ molecules by heating the metal enough so that becomes gaseous. Either find a chamber that resists temperatures of around $\mathrm{4000\ K}$ to get a decently high vapour pressure, or more likely, do some kind of ablation (plasma, laser, etc) on solid uranium, though there would probably be contamination with larger metallic clusters. – Nicolau Saker Neto Mar 3 '16 at 9:11