370There are also stannates with the structure [Sn(OH) 6 ]2−, like K 2 [Sn(OH) 6 ], although the free
stannic acid H 2 [Sn(OH) 6 ] is unknown. The sulfides of tin exist in both the +2 and +4
oxidation states: tin (II) sulfide and tin (IV) sulfide (mosaic gold).
Hydrides
Stannane (SnH 4 ), where tin is in the +4 oxidation state, is unstable. Organotin hydrides
are however well known, e.g. tributyltin hydride (Sn(C 4 H 9 ) 3 H). These compound release
transient tributyl tin radicals, rare examples of compounds of tin (III).
Organotin Compounds
Organotin compounds, sometimes called stannanes, are chemical compounds with tin-
carbon bonds. Of the compounds of tin, the organic derivatives are the most useful
commercially. Some organotin compounds are highly toxic and have been used as
biocides. The first organotin compound to be reported was diethyltin diiodide ((C 2 H 5 ) 2 SnI 2 ),
reported by Edward Frankland in 1849.
Most organotin compounds are colorless liquids or solids that are stable to air and water.
They adopt tetrahedral geometry. Tetraalkyl- and tetraaryltin compounds can be prepared
using
Grignard reagents:
SnCl 4 + 4 RMgBr → R 4 Sn + 4 MgBrCl
The mixed halide-alkyls, which are more common and more important commercially than
the tetraorgano derivatives, are prepared by redistribution reactions:
SnCl 4 + R 4 Sn → 2 SnCl 2 R 2Divalent organotin compounds are uncommon, although more common than related
divalent organogermanium and organosilicon compounds. The greater stabilization
enjoyed by Sn(II) is attributed to the "inert pair effect". Organotin(II) compounds include
both stannylenes (formula: R 2 Sn, as seen for singlet carbenes) and distannylenes (R 4 Sn 2 ),
which are roughly equivalent to alkenes. Both classes exhibit unusual reactions.