${}^{119}\text{S}\text{n}$ spin-lattice relaxation in $\alpha {\text{-SnF}}_2$

The temperature and magnetic field dependencies of the ${}^{119}\text{S}\text{n}$ nuclear spin-lattice relaxation rate in $\alpha {\text{-SnF}}_2$ indicate the presence of two relaxation mechanisms. At temperatures below 350 K, the relaxation is dominated by a nuclear spin-rotation interaction modulated by lattice vibrations, as has been seen for Pb and Tl salts. This ${}^{119}\text{S}\text{n}$ relaxation pathway is less effective in ${\text{SnF}}_2$ than it is for ${}^{207}\text{P}\text{b}$, ${}^{203}\text{T}\text{l}$, and ${}^{205}\text{T}\text{l}$ relaxation in some Pb and Tl salts but it is more effective than ${}^{111}\text{C}\text{d}$ and ${}^{113}\text{C}\text{d}$ relaxation in some Cd salts. Above 350 K, there is an additional contribution to the observed relaxation rate. The most likely candidate for this thermally activated contribution is the modulation of the ${}^{119}\text{S}\text{n-}{}^{19}\text{F}$ dipolar interaction by fluoride-ion motion.

Figure 1

(Color online) The crystal structure of $\alpha {\text{-SnF}}_2$. There are two inequivalent Sn sites as indicated (blue and black colored beach balls online) and there are four inequivalent F sites as indicated (four different solid colors online). The tetramer ${\text{Sn}}_4{\text{F}}_8$ is indicated by solid lines. (a) The (010) plane based on Fig. 2 of Ref. 16. (b) The (100) plane based on Fig. 3 of Ref. 16. The same tetramer is indicated in both parts. There are four such tetramers in the unit cell, which is indicated. The structure was taken from the inorganic structure database (Ref. 19) and the figure was made using CRYSTALMAKER.

Figure 2

The ${}^{119}\text{S}\text{n}$ NMR spectrum of a polycrystalline sample of ${\text{SnF}}_2$ at 295 K and 74.6 MHz.

Figure 3

(Color online) The ${}^{119}\text{S}\text{n}$ spin-lattice relaxation rate constant, $R$, in ${\text{SnF}}_2$ as a function of $T^2$ at 74.6 and 111.9 MHz. The straight line is given by Eq. (2) and the top line is given by Eqs. (2, 3), both with parameters given in the text.

Figure 4

(Color online) The difference between the observed relaxation rates and the $A{T}^2$ term (the straight line in Fig. 3) in Eq. (2). The straight lines are given by Eq. (3) for the 74.6 MHz data, the 111.9 MHz data, and both data sets taken as one, with parameters given in the text.