Tin-119 Mössbauer and nuclear magnetic resonance studies of organotin compounds. Part 1. Sterically crowded tetraorganotin derivatives

Abstract

¹¹⁹ Sn Mössbauer and ¹¹⁹Sn n.m.r. data are presented for a series of sterically hindered tetra-organotin derivatives. For adamant-1-yl (ad) derivatives two quadrupole splittings (q.s.) are observed and the values of the tin chemical shifts, δ(¹¹⁹Sn), are significantly more negative (resonances at higher field) than expected. Thus Sn(ad)₄ shows the presence of q.s. with values of 2.70 and 0.76 mm s^–1 at 80 K. These tin sites are discussed. The δ(¹¹⁹Sn) value of –73.5 p.p.m. (relative to SnMe₄) indicates increased electron density at the tin atom probably resulting from charge separation of the type ad₃[graphic omitted]. Other sterically hindered derivatives show similar features, although less dramatically. The additivity effect of tin substituents in this series is also discussed. Long relaxation times were recorded for the more sterically hindered derivatives. The Mössbauer spectrum at 80 K for quench-frozen SnPh₄ is also presented. The spectrum shows a singlet with a large linewidth, which narrows on annealing at 193 K to give a very narrow line. The wide line is easily explained in terms of the known crystal structure.