Structural studies of 4,5,6,7-tetrabromobenzimidazole derivatives by means of solid-state 13C, 15N NMR spectroscopy and DFT calculations

Abstract Tetrabromobenzimidazole derivatives containing sulfur or nitrogen atom in a five- or six-membered saturated ring were synthesized as potential ligands of casein kinase (CK2). Structural data of these compounds are crucial for understanding their inhibitory activity as inhibitors. Solution and solid-state 13 C NMR spectra were recorded for six compounds, and 15 N MAS spectra – for two of them. 13 C CPMAS spectra were assigned by comparison with solution data and with the aid of dipolar dephasing and variable contact time experiments. The correctness of assignments of 13 C and 15 N chemical shifts was verified by GIAO DFT calculations of shielding constants. The differences between the solution and solid-state chemical shift values were explained in terms of intermolecular interactions. The doublet resonances occurring in the solid-state 13 C and 15 N NMR spectra of N 1 , N 2 -propylene-2-amino-4,5,6,7-tetrabromobenzimidazole indicate the presence of two molecules in crystallographic unit cell. Shielding constants calculated for a dimer with two N1′ H…N3 hydrogen bonds suggest that the association type does not influence carbon shielding. The coexistence of two tautomers with N1′ H and N3 H is less probable.