When tin is combined with an alkali or alkaline earth metal some of the compounds formed have ionic structures containing monatomic or polyatomic tin anions (Zintl ions), such as Sn4− in Mg2Sn[2] or Sn4−9 in K4Sn9.
[3] Even with these metals not all of the compounds formed can be considered to be ionic with localised bonding, for example Sr3Sn5, a metallic compound, contains {Sn5} square pyramidal units.
Niobium stannide, Nb3Sn is perhaps the best known superconducting tin intermetallics.
There are multiple rare earth stannides, including with dysprosium and yttrium.
Some examples of stannide Zintl ions are listed below.