Potentiometric speciation studies, mass spectrometry, and DFT calculations helped to predict the various structural possibilities of the dinuclear trivalent lanthanide ion (LnIII, 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 TbIII to EuIII ion. The internuclear distance RTbEu 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 kobs data was performed using the equation: kobs,corr.=kobs−kobs,OH=kLn2LHM->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.