Dinuclear Lanthanide(III)-m-ODO2A-dimer Macrocyclic Complexes: Solution Speciation, DFT Calculations, Luminescence Properties, and Promoted Nitrophenyl-Phosphate Hydrolysis Rates

Potentiometric speciation studies, mass spectrometry, and DFT calculations helped to predict the various structural possibilities of the dinuclear trivalent lanthanide ion (Ln^III, Ln=La, Eu, Tb, Yb, Y) complexes of a novel macrocyclic ligand, m-ODO2A-dimer (H₄L), to correlate with their luminescence properties and the promoted BNPP and HPNP phosphodiester bond hydrolysis reaction rates. The stability constants of the dinuclear Ln₂(m-ODO2A-dimer) complexes and various hydrolytic species confirmed by mass spectrometry were determined. DFT calculations revealed that the Y₂LH₋₁ and the Y₂LH₋₂ species tended to form structures with the respective closed- and open-form conformations. Luminescence lifetime data for the heterodimetallic TbEuL system confirmed the fluorescence resonance energy transfer from the Tb^III to Eu^III ion. The internuclear distance R_TbEu values were estimated to be in the range of 9.4–11.3 Å (pH 6.7–10.6), which were comparable to those of the DFT calculated open-form conformations. Multiple linear regression analysis of the k_obs data was performed using the equation: k_obs,corr.=k_obs−k_obs,OH=k_Ln2LHM^->1 [Ln₂LH₋₁]+k _Ln2LH-2 [Ln₂LH₋₂] for the observed Ln₂L-promoted BNPP/HPNP hydrolysis reactions in solution pH from 7 to 10.5 (Ln=Eu, Yb). The results showed that the second-order rate constants for the Eu₂LH₋₂ and Yb₂LH₋₂ species were about 50–400 times more reactive than the structural analogous Zn₂(m-12 N₃O-dimer) system.