Five-coordinate organotin complexes

The 119Sn chemical shifts of some discrete five- and six-coordinate organotin complexes are collected in Table X. 

Reported changes in chemical shift (50) with temperature and concentration of trimethyltin chloride in methanol or ethanol indicate a more complicated process than a simple monomer complex equilibrium. It has been suggested that ionization of the organotin compound occurs in these solvents, probably forming a solvated five-coordinate (RjSnLz) cationic species. 

The five-coordinate complexes of type 421 possess a rigid structure, which is retained in solution as indicated by comparing the Sn NMR in solution and in the solid state . For 421a-c, isotope-induced chemical shifts A ( C( Sn) were determined for the first time for five-coordinate tin nuclei at natural abundance of A positive sign of 1 Ai2/i3c(ii Sn) was found, in contrast with most tetracoordinate organotin compounds. 

Five reviews have appeared entitled A mechanistic investigation of gelation. The sol-gel polymerization of precursors to bridged polysilsequioxanes , which contains Si NMR data, Derivatives of hydroxamic acids , which contains Si NMR data, A primer on the aqueous chemistry of silicon , which contains Si NMR data, Organotin(IV) complexes of amino acids and peptides , which contains Sn NMR data, and Novel reaction system using highly coordinated organotin enolates . ... 

The structural chemistry of the organotin halides is dominated by their Lewis acid properties and their propensity to form five- and six-coordinate complexes. Self-association may give oligomers or polymers in the solid state, which usually dissociate in solution. The structure of tricyclohexyltin chloride in the crystal is temperature-dependent. At 108 K, it has the form of a rod-like polymer with distorted trigonal-bipyramidal tin and Sn-Cl separations of 245.6(7) and 300.77(7) pm, but at 298 K, the structure is best regarded as consisting of near-tetrahedral discrete molecules.3... 

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