Figure 3.

500 MHz ¹H NMR spectra of sample A (b) and sample B (a) dissolved in acetonitrile-d₃. The red inset shown in the middle of the spectrum represents N–H protons. The spectra were recorded at a temperature of 298 K. ¹H–¹⁵N HSQC 2D NMR correlations for sample B (c) and for sample A (d). Sample were dissolved in acetonitrile-d₃. Symbol S (d) represents sample with symmetrical geometry, symbol U represents unsymmetrical sample.