If there is bonding between two atoms where one atom is
having one vaant orbital and another is having one lone pair of electrons, then
if this electron pair is donated to that respective vacant orbital then the
bonding is called p (pie) – p (pie) or p (pie ) – d ( pie) depending on the
orbital to which the electron pair is donated and from which the electron pair
is donated. If both the orbitals are d orbitals , then bonding is called d (pie) – d(pie) bonding .