The formation stability, hydrolytic behavior, mass spectrometry, DFT study, and luminescence properties of trivalent lanthanide complexes of H sub(2)ODO2A

The trivalent lanthanide complex formation constants (log K sub(f)) of the macrocyclic ligand H sub(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 sub(2)DO2A (1,7-dicarboxylmethyl-1,4,7,10-tetraazacyclododecane) complexes. The equilibrium formation of the dinuclear hydrolysis species, e.g. Ln sub(2)(ODO2A) sub(2)( mu -OH) super(+) and Ln sub(2)(ODO2A) sub(2)( mu - OH) sub(2), dominates over the mononuclear species, e.g. LnODO2A(OH) and LnODO2A(OH) sub(2) super(-). Mass spectrometry confirmed the presence of [Eu(ODO2A)] super(+), [Eu(ODO2A)(OH)+H] super(+), [Eu sub(2)(ODO2A) sub(2)(OH sub(2)) sub(2)+H] super(+), [Eu(ODO2A)(OH) sub(2)] super(-) and [Eu sub(2)(ODO2A) sub(2)(OH sub(2)) sub(3)] super(-) species at pH > 7. Density function theory (DFT) calculated structures of the EuODO2A(H sub(2)O) sub(3) super(+) and EuDO2A(H sub(2)O) sub(3) super(+) complexes indicate that three inner-sphere coordinated water molecules are arranged in a meridionalconfiguration, i.e.the 3 water molecules are on the same plane perpendicular to that of the basal N sub(3)O or N sub(4) atoms. However, luminescence lifetime studies reveal that the EuODO2A super(+) and TbODO2A super(+) complexes have 4.1 and 2.9 inner-sphere coordinated water molecules, respectively, indicating that other equilibrium species are also present for the EuODO2A super(+) complex. The respective emission spectral intensities and lifetimes at 615 nm ( lambda sub(ex) = 395 nm) and 544 nm ( lambda sub(ex) = 369 nm) of the EuODO2A super(+) and TbODO2A super(+) complexes increase with increasing pH, consistent with the formation of mu -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 sub(2)(ODO2A) sub(2)( mu -OH)(H sub(2)O) sub(2)] super(+), trans-[Y sub(2)(ODO2A) sub( 2)( mu -OH)(H sub(2)O) sub(2)] super(+) and [Y sub(2)(ODO2A) sub(2)( mu - OH) sub(2)] dinuclear complex structures. The first and the second include 6-coordination by the ligand ODO2A super(2-), one by the bridged mu -OH ion and one by a water molecule. The third includes 6-coordination by the ligand ODO2A super(2-) and two by the bridged mu -OH ions. The two inner-sphere coordinated water molecules in the cis- and trans-[Y sub(2)(ODO2A) sub( 2)( mu -OH)