Spectroscopic and Related Properties

Quantum mechanical methods have been used to calculate Sn NMR properties such as chemical shifts and coupling constants, for stannane, tetramethylstannane, methyltin halides, tin halides, and some stannyl cations. Relativistic effects were included by using the ZORA method. Each method allows the possibility of including only scalar effects or spin orbit coupling as well. Sn chemical shifts and spin-spin couplings were calculated and compared to experimental values. A favorable correlation was shown for the chemical shifts, except for organotin species where heavy atoms are bound to tin, in which case a good correlation was obtained only at the spin-orbital level. Therefore, it is clear that relativistic effects must be considered for these heavy-element tin systems. 

Many of the recent studies that examine Raman and infrared spectroscopy have been mentioned in previous sections of this chapter.However, a vibrational spectroscopic smdy by Comerlato and coworkers used HE and B3LYP with the SBKJC EPC for tin to examine IR and Raman spectra of the anionic [NEt4]2[Sn(dmit)3] complex. Comparison of the calculated scaled frequencies to experimental values revealed that the B3LYP method is more accurate than the HE method. The latter method is well known to overestimate frequencies by about 10%. 

Other related chemical properties of organotin systems are also of recent interest, including dipole po-larisability and second hyperpolarisability, atomic charge, electrostatic potential, ionization potentials, electron affinities, and electronegativities.  

RJB and TBG gratefully acknowledge the Natural Sciences and Engineering Research Council of Canada (NSERC) for financial support. 

Jensen, Introduction to Computational Chemistry, John Wiley Sons Ltd., Chichester, UK, 2007. 

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Spectroscopic and Related Properties of Thiols.— The n.m.r. absorption of the thiol proton moves to lower field in the order PhCHa SH, PhjCH SH, PhaC SH corresponding hydrotrisulphides RSS SH show the opposite sequence, due to over-riding inductive and anisotropic effects within the cumulative sulphur chain. 

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