Uranyl complexation by monodentate nitrogen donor ligands. A relativistic density functional study

To examine the interaction of uranyl with nitrogen containing groups of humic substances, the model complexes [UO₂(H₂O)₄L_N]²⁺, L_N = NH₂CH₃, N(CH₃)₃, and NC₅H₅ in aqueous solution were studied computationally with an all‐electron relativistic density functional method. Results are compared with the corresponding penta‐aqua complex of uranyl. Although pyridine coordinates with about the same strength as L = H₂O, methylamine binds ～10 kJ mol^?1 stronger and trimethylamine ～40 kJ mol^?1 weaker than a fifth aqua ligand. Yet, each of these ligands L_N donates about the same amount of charge to uranyl as L = H₂O. U? N bonds are ～10 pm longer than the U? O bonds of the aqua ligands. From the present model results, one does not expect that, when compared with carboxyl groups, monodentate N‐containing functional groups contribute significantly to uranyl complexation by humic substances. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011