DFT study of 2,9-bis(1,2,4-triazin-3-yl)-1,10-phenanthroline (BTPhen) and its derivatives complexation with lanthanide series

•Five BTPhen derivatives were studied to better understand lanthanide complextion.•Studied complexes contained two ligands and one lanthanide 3+ ion.•Substituting the outer nitrogen of triazine group increases the complex stability.•Substituting the inner nitrogen of triazine group lowers the complex stability.