Stannide - Stannide, Sn_xy- Ions

Stannide, Sn_xy- Ions

Some examples of stannide Zintl ions are listed below. Some of them contain 2 centre- 2 electron bonds (2c-2e), others are "electron deficient" and bonding sometimes can be described using polyhedral skeletal electron pair theory (Wade's Rules) where the number of valence electrons contributed by each tin atom is considered to be 2 (the s electrons do not contribute). There are some examples of silicide and plumbide ions with similar structures, for example tetrahedral Si₄4−, the chain anion {Si2−)_n, Pb₄4− and Pb₉4−.

• Sn4− found for example in Mg₂Sn
• Sn₄4−, tetrahedral with 2c-2e bonds e.g. in CsSn.
• Sn₄2−, tetrahedral closo- cluster with 10 electrons (2n+2)
• {Sn2−)_n zig-zag chain polymeric anion with 2c-2e bonds found for example in BaSn
• Sn₅2−closo-cluster, 12 electrons (2n+2), (i.e. trigonal bipyramidal) in (2,2,2-crypt-Na)₂Sn₅
• (Sn₈4−)_n polymeric "2-D" anion in NaSn₂
• Sn₉4− nido-cluster 22 electrons, (2n+4)(capped square antiprismatic) with as per polyhedral skeletal electron pair theory, in the intermetallic K₄Sn₉, and a distorted ion in the salt Na₄Sn₉.7en (en = ethylenediamine)
• Sn₉3− a paramagnetic, 21 electrons, closo- cluster anion ( D_3h symmetry)( 1 more electron than the 20 (2n+2) predicted by polyhedral skeletal electron pair theory
• (Sn₁₂7−)_n polymeric "2-D" anion in Na₇Sn₁₂