Stannide

A stannide can refer to an intermetallic compound containing tin combined with one or more other metals; an anion consisting solely of tin atoms or a compound containing such an anion, or, in the field of organometallic chemistry an ionic compound containing an organotin anion. An alternative name for such a compound is stannanide.

Binary alkali and alkaline earth stannides

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 Sn^{4−} in Mg₂Sn or in K₄Sn₉. 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.

Ternary alkali and alkaline earth stannides

Ternary (where there is an alkali or alkaline earth metal, a transition metal as well as tin e.g. LiRh₃Sn₅ and MgRuSn₄) have been investigated.

Other metal stannides

Binary (involving one other metal) and ternary (involving two other metals) intermetallic stannides have been investigated. Niobium stannide, Nb₃Sn is perhaps the best known superconducting tin intermetallics. This is more commonly called "niobium-tin".

There are multiple rare earth stannides, including with dysprosium and yttrium.

Stannide 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 , the chain anion (Si^{2−})_n, and .

• Sn^{4−} found for example in Mg₂Sn.
• , tetrahedral with 2c-2e bonds e.g. in CsSn.
• , tetrahedral closo-cluster with 10 electrons (2n + 2).
• (Sn^{2−})_n zig-zag chain polymeric anion with 2c-2e bonds found for example in BaSn.
• closo-cluster, 12 electrons (2n + 2), (i.e. trigonal bipyramidal) in (2,2,2-crypt-Na)₂Sn₅.
• polymeric two-dimensional anion in NaSn₂.
• 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 Na₄Sn₉·7 en.
• 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.
• polymeric two-dimensional anion in Na₇Sn₁₂

References