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

[Display omitted] •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. The complexation reactions between lanthanide 3+ cations and 2,9-bis(1,2,4-triazin-3-yl)-1,10-phenanthroline and its derivatives were studied with density functional theory Perdew-Burke-Ernzerhof functionals. The complexes consisted of one lanthanide cation and two ligand molecules. Complexation reactions were found to be exothermic and spontaneous in the gas phase. Absolute values of complextion energy and enthalpy increase in the lanthanide series and follow linear trends of lanthanide atomic number. All the bond lengths decrease in the lanthanide series with increasing charge density.