Properties of Polystannanes

The electronic spectra of the linear oligostannanes e.g. for the homologous series Et3Sn-(SnEt2)n-SnEts, (n = 0 ) are detailed in Tables 3.8.2 and 3.8.3. They exhibit a systematic red shift of the lowest energy transition, which is associated with a cr-cr transition, upon increasing the chain length. Eor example, the T- ax for perethylated distannane is red shifted from 232 nm to 325 nm for hexastannane. 

The poly(stannane-co-germane) and poly(stannane-co-silane) materials exhibit kmax between those of the respective homopolymers. However, increasing the stannane contents in the copolymers results in a red shift of the UV absorption probably due to the effective overlap of orbitals ascribed to the increased atomic radius of tin over Ge(Si). As an example, for poly(di-n-butylstannane-ct -di-n-butylsilane) with an Sn Si ratio of 43 57, kmax = 375 nm, as compared to 314 and 384 nm for poly(di-n-butylsilane) and poly(di-n-butylstannane), respectively. 

The poly(dialkyl) stannanes, (Hex2Sn) and (Oct2Sn) exhibit a reversible thermochromic behavior upon warming above room temperature. The A. iax values of these polymers undergo a blue-shift from 384 to 369 nm for poly(di-n-octyl)stannane between 30 0 °C in toluene and from 392 to 382 nm in 

Polystannanes are routinely characterized by and spectroscopy, and (GPC) against polystyrene standards of different molecular weights in THF. However, it is often Sn NMR in particular that is a valuable tool to determine the structure of the linear oligomeric and polymeric chains and provides useful information regarding purity of polymer chains and ratios and types of cyclic oligomers. 

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