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Dalton Trans. 2012 Dec 28;41(48):14697-706. doi: 10.1039/c2dt31479g.

The formation stability, hydrolytic behavior, mass spectrometry, DFT study, and luminescence properties of trivalent lanthanide complexes of H2ODO2A.

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  • 1Department of Biological Science and Technology, National Chiao Tung University, No. 75 Po-Ai Street, Hsinchu, Taiwan 30039, ROC. cachang@ym.edu.tw

Abstract

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.

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