Vnmrs 400 mhz nmr spectrometer

¹H and ¹³C NMR measurements
were conducted on 1, aged 2, and 3 dissolved in DMSO-d₆ at a concentration
of 9.5, 9, and 0.6 wt %,
respectively. The ¹H and ¹³C NMR spectra were
collected on a Bruker Avance NEO 500 MHz NMR spectrometer. ¹H spectra were collected with a sweep width of 11 904.8 Hz;
a relaxation delay of 5 s and 32 signal averages and referenced internally
to the chemical shift of the tetramethylsilane. ¹³C spectra
were collected with a sweep width of 34 246.6 Hz, a relaxation
delay of 2 s, and 256 signal averages and referenced to the chemical
shift of the solvent, DMSO-d₆ (39.5 ppm). ⁷⁷Se NMR measurements were conducted using a Varian VNMRS 400
MHz NMR spectrometer on 1 dissolved in DMSO-d₆ at a concentration of 9.5 wt %. ⁷⁷Se NMR
spectra were collected with a sweep width of 37 878.8 Hz, a
relaxation delay of 6 s, and 48 signal averages. A 0.5 M solution
of dimethyl diselenide in CDCl₃ was used as an external
chemical shift reference (269 ppm).^{40 (link)} Moreover, ⁷⁷Se NMR measurements were conducted on diphenyl diselenide
dissolved in DMSO-d₆ at a concentration
of 10 wt %.