31P solid-state nuclear magnetic resonance (NMR) spectra of 12 metal-containing selenophosphates have been examined to distinguish between the [P2Se6]4-, [PSe4]3-, [P4Se10]4-, [P2Se7]4-, and [P2Se9]4- anions. There is a general correlation between the chemical shifts (CSs) of anions and the presence of a P-P bond. The [P2Se6]4- and [P4Se10]4- anions both contain a P-P bond and resonate between 25 and 95 ppm whereas the [PSe4]3-, [P2Se7]4-, and [P2Se9]4- anions do not contain a P-P bond and resonate between -115 and -30 ppm. The chemical shift anisotropies (CSAs) of compounds containing [PSe4]3- anions are less than 80 ppm, which is significantly smaller than the CSAs of any of the other anions (range: 135-275 ppm). The smaller CSAs of the [PSe4]3- anion are likely due to the unique local tetrahedral symmetry of this anion. Spin-lattice relaxation times (T1) have been determined for the solid compounds and vary between 20 and 3000 s. Unlike the CS, T1 does not appear to correlate with P-P bonding. 31P NMR is also shown to be a good method for impurity detection and identification in the solid compounds. The results of this study suggest that 31P NMR will be a useful tool for anion identification and quantitation in high-temperature melts.
ASJC Scopus subject areas
- Inorganic Chemistry