A. Laaksonen et Re. Wasylishen, AN ABSOLUTE CHEMICAL SHIELDING SCALE FOR TIN FROM NMR RELAXATION STUDIES AND MOLECULAR-DYNAMICS SIMULATIONS, Journal of the American Chemical Society, 117(1), 1995, pp. 392-400
An approximate nuclear magnetic shielding scale for tin has been obtai
ned from Sn-119 spin-rotation constants, C-eff(Sn-119), in a series of
spherical top molecules (SnX(4), X = H, D, CH3, and Cl). The paramagn
etic shielding at a nucleus induced by circulating charge is known to
be intimately related to the nuclear spin-rotation constant. Tin-119 s
pin-rotation constants in stannane, SnH4, have been determined by two
independent techniques. In the first, C-eff(Sn-119) has been obtained
from the experimentally determined ratio of the H-1 and Sn-119 spin-la
ttice relaxation times of gaseous stannane, T-1(H-1)/T-1(Sn-119) = 657
0 +/- 600, and the known effective H-1 spin-rotation constant for meth
ane. The second technique involved combining experimental T-1(Sn-119)
data for liquid SnH4, SnD4, Sn(CH3)(4), and SnCl4 with angular momentu
m correlation times, tau(J)'s, calculated from molecular dynamics (MD)
simulations. Since the spin-rotation relaxation mechanism is the only
important mechanism for Sn-119 T-1 relaxation in these compounds, val
ues of C-eff(Sn-119) were readily determined from the experimental liq
uid-phase T-1(Sn-119) data and the MD simulations. The tin relaxation
data for liquid tetramethyltin and tin tetrachloride were taken from t
he literature, while T-1 data for SnH4 and SnD4 were obtained in the p
resent study. Consideration of all the spin-rotation constant data obt
ained in this study indicates that the tin shielding constant, sigma(S
n), in liquid tetramethyltin is 2180 +/- 200 ppm with respect to the b
are nucleus. The absolute nuclear shielding values obtained for tin in
this study are compared to values recently obtained from quantum mech
anical calculations. On the basis of the results of the present study,
the Sn-119 magnetogyric ratio, gamma(Sn.119), is -9.997 559(8) x 10(7
) rad s(-1) T-1, approximately 3% less than the accepted value.