$Fe \left( NO _{2}\right)_{3} Cl _{3}$ and $Fe ( ONO )_{3} Cl _{3}$ show linkage isomerism. This type of isomerism is shown by the complexes in which an ambidentate ligand is present. $NO _{2}^{-}, SCN ^{-}, CN ^{-}$etc are ambidentate ligand as each of them contain more than one donor site.
In the linkage isomerism, at a time only one donor atom of ligand is borded to metal atom and hence, arises linkage isomerism.