Laser-Induced Luminescence Studies and Crystal Structure of the Europium(III) Complex of 1,4,7,10-Tetrakis(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane. The Link between Phosphate Diester Binding and Catalysis by Lanthanide(III) Macrocyclic Complexes

Solution and solid-state properties of the Eu(III) complex of the tetramide macrocyclic ligand TCMC (TCMC = 1,4,7,10-tetrakis(carbamoylmethyl)-1,4-7,10-tetraazacyclododecane) are investigated as part of an effort to develop lanthanide(III) macrocyclic catalysts. (Eu(TCMC)(H{sub 2}O))(CF{sub 3}SO{sub 3}){sub 3}{center_dot}2CH{sub 3}OH crystallizes in the centrosymmetric monoclinic space group. The structure was solved and refined to R=4.02% and R{sub w}=4.33% for 3510 reflections with F>6{omega}(F). (R=7.04%, R{sub w}=6.48% for all 5322 independent reflections). Four stereoisomers (two enantiomeric pairs) of the (Eu(TCMC)(H{sub 2}O)){sup 3+} cation appear in the crystal. The structure is disordered, containing two overlapping diastereomers that are interrelated by different conformations of the 1,4,7,10-tetraazacyclododecane ring defining the asymmetric unit. Two enantiomers are related to these by operations of the second king (i,n-glide). The nine-coordinate Eu(III) center has a 4:4:1 coordination geometry formed by the octadentate TCMC ligand and a single bound water molecule. The laser-induced luminescence excitation band of a single crystal of (Eu(TCMC)H{sub 2}O)(CF{sub 3}SO{sub 3}){sub 3}{center_dot}2CH{sub 3}OH resolves into two peaks, suggesting that each diastereomer gives rise to a separate excitation peak. Similarly, the luminescence excitation spectrum of a solution of (Eu(TCMC)){sup 3+} in water indicates that two species are present in solution. The {sup 31}P NMR resonance of diethyl phosphate is monitored atmore » 18{+-}2{degrees}C, pH 7.4, upon addition of (Eu(TCMC)){sup 3+} as well as upon addition of several lanthanide(III) complexes that are catalysts for RNA cleavage. No binding of diethyl phosphate to (Eu(TCMC)){sup 3+} is observed. The hexadentate Schiff-base complex (La(L{sup 1})){sup 3+} binds to diethyl phosphate with a binding constant of 47.7{+-}0.5 M{sup -1}.« less