Structural characterization of 6,6′-bis(substituted)-5,5′-bi-1,2,4-triazines as potential N-heterocyclic ligands for the extraction of nuclear waste

Novel disubstituted 5,5′-bi-1,2,4-triazines bearing pyridine (1), furan (2) and thiophene (3) rings at 6 and 6′-positions of the parent bitriazine were prepared as potential extractants of nuclear waste. The compounds were easily obtained by Stille coupling starting from 6,6′-bisbromo-3,3′-bis(N,N-dimethylamine)-5,5′-bi-1,2,4-triazine and the corresponding tin reagents. The molecular and crystal structures of the ligands 1–3 were determined by the X-ray analysis. The X-ray investigations show different conformations of the molecules described as gauche–gauche–gauche for 1 and gauche–cis–cis for 2 and 3. Each of the molecules resides on a twofold axis that passes through the middle of the central C5–C5′ bond. The molecular packing in 1 is influenced by the π⋯π and weak C–H⋯π interactions. The crystal structures of 2 and 3 are governed by a combination of a weak C–H⋯N hydrogen bonds and C–H⋯π interactions. Theoretical calculations using semi-empirical AM1 and DFT/B3LYP/6-311++G(d,p) ab initio methods were carried out to find correlation between conformational and electronic parameters of the molecules and their preferences to metal ions complexations.