The formation stability, hydrolytic behavior, mass spectrometry, DFT study, and luminescence properties of trivalent lanthanide complexes of H2ODO2AElectronic supplementary information (ESI) available. See DOI: 10.1039/c2dt31479g

The trivalent lanthanide complex formation constants (log K f ) of the macrocyclic ligand H 2 ODO2A (4,10-dicarboxymethyl-1-oxa-4,7,10-triazacyclododecane) have been determined by pH titration techniques to be in the range 10.84-12.62 which increase with increasing lanthanide atomic number, and are smaller than those of the corresponding H 2 DO2A (1,7-dicarboxylmethyl-1,4,7,10-tetraazacyclododecane) complexes. The equilibrium formation of the dinuclear hydrolysis species, e.g. Ln 2 (ODO2A) 2 (μ-OH) + and Ln 2 (ODO2A) 2 (μ-OH) 2 , dominates over the mononuclear species, e.g. LnODO2A(OH) and LnODO2A(OH) 2 − . Mass spectrometry confirmed the presence of [Eu(ODO2A)] + , [Eu(ODO2A)(OH)+H] + , [Eu 2 (ODO2A) 2 (OH 2 ) 2 +H] + , [Eu(ODO2A)(OH) 2 ] − and [Eu 2 (ODO2A) 2 (OH 2 ) 3 ] − species at pH > 7. Density function theory (DFT) calculated structures of the EuODO2A(H 2 O) 3 + and EuDO2A(H 2 O) 3 + complexes indicate that three inner-sphere coordinated water molecules are arranged in a meridional configuration, i.e. the 3 water molecules are on the same plane perpendicular to that of the basal N 3 O or N 4 atoms. However, luminescence lifetime studies reveal that the EuODO2A + and TbODO2A + complexes have 4.1 and 2.9 inner-sphere coordinated water molecules, respectively, indicating that other equilibrium species are also present for the EuODO2A + complex. The respective emission spectral intensities and lifetimes at 615 nm ( λ ex = 395 nm) and 544 nm ( λ ex = 369 nm) of the EuODO2A + and TbODO2A + complexes increase with increasing pH, consistent with the formation of μ-OH-bridged dinuclear species at higher pH. Additional DFT calculations show that each Y( iii ) ion is 8-coordinated in the three possible cis -[Y 2 (ODO2A) 2 (μ-OH)(H 2 O) 2 ] + , trans -[Y 2 (ODO2A) 2 (μ-OH)(H 2 O) 2 ] + and [Y 2 (ODO2A) 2 (μ-OH) 2 ] dinuclear complex structures. The first and the second include 6-coordination by the ligand ODO2A 2− , one by the bridged μ-OH ion and one by a water molecule. The third includes 6-coordination by the ligand ODO2A 2− and two by the bridged μ-OH ions. The two inner-sphere coordinated water molecules in the cis - and trans -[Y 2 (ODO2A) 2 (μ-OH)(H 2 O) 2 ] + dinuclear complexes are in a staggered conformation with torsional angles of 82.21° and 148.54°, respectively. The equilibrium formation of the dinuclear lanthanide hydrolytic species, Ln 2 (ODO2A) 2 (μ-OH) + and Ln 2 (ODO2A) 2 (μ-OH) 2 , dominates over the mononuclear species, LnODO2A(OH) and LnO