Oxo ligand
= Oxo ligand
{title2=$\mathrm O^{2-}$}
A coordinated oxide, formally $\mathrm O^{2-}$. A terminal $\mathrm{M{=}O}$ unit is conventionally counted as an $X_2$ ligand giving four <electrons> in ionic <electron counting>. Additional oxygen-to-metal <pi donation> is an orbital-bonding issue and must not be silently mixed with another counting convention.