Synthesis and electrochemistry of mono- and binuclear europium complexes with the macrocyclic ligand 1,4,7,10,14,17,20,23-octaazacyclohexacosane-1,4,7,10,14,17,20,23-octaacetic acid (OHEC)

Unexpected Differences in the Dynamics and in the Nuclear and Electronic Relaxation Properties of the Isoelectronic [EuII(DTPA)(H2O)]3-and [GdIII(DTPA)(H2O)]2-Complexes (DTPA = Diethylenetriamine Pentaacetate)1

“…From the electrode potentials obtained above pH = 6 for the [Eu II (DTPA)(H 2 O)] 3- /[Eu III (DTPA)(H 2 O)] 2- system, E 1/2 , one can calculate the stability constant of the [Eu II (DTPA)(H 2 O)] 3- complex by using the known stability constant of [Eu III (DTPA)(H 2 O)] 2- (log K III = 22.39) 19 and the potential of the Eu 2+ (aq) /Eu 3+ (aq) redox couple, E ‘ 1/2 , and considering eqs 1−6 The Nernst equations for the redox couple Eu 2+ (aq) /Eu 3+ (aq) and [Eu II (DTPA)(H 2 O)] 3- /[Eu III (DTPA)(H 2 O)] 2- are given in eqs 1 and 2, respectively: The stability constants of the two complexes are expressed by eqs 3 and 4: Insertion of eqs 3 and 4 into eq 2 yields After making the general assumption of E ‘ 0 1/2 = E 0 1/2 , , we obtain The stability constant obtained in this way is log K II = 9.94 (25 °C; I = 0.5 M), which corresponds well to the value previously determined by pH potentiometry, log K II = 10.08 (25 °C; I = 1 M KCl) . The electrochemical data also confirm that at higher pH only the nonprotonated species is present in solution, which is in accordance with the p K a = 5.45 value published in the literature (see Figure S2, Supporting Information) …”

Lanthanide-Containing Molecular and Supramolecular Polymetallic Functional Assemblies

“…For instance, in catalysis, (i) facile oxidation of phenols in the presence of a dicerium(IV) complex of calix[8]arene was demonstrated 180 and (ii) improved rates were found for the cleavage of phosphodiester bonds in DNA and RNA (see section II.A). The redox potential may also be affected, as shown by the dimetallic Eu(III) complex of an octaazacyclohexacosane octaacetic acid macrocycle which undergoes a two-electron reduction to Eu(II) at a more cathodic potential than the one-electron reduction of the monometallic complex . Mixed oxidation state species Ln(II)−Ln(III) have also been isolated (particularly with Yb and Sm), for instance, with a terbutylated pyrazolate .…”

“…The redox potential may also be affected, as shown by the dimetallic Eu(III) complex of an octaazacyclohexacosane octaacetic acid macrocycle which undergoes a two-electron reduction to Eu(II) at a more cathodic potential than the one-electron reduction of the monometallic complex. 181 Mixed oxidation state species Ln(II)-Ln(III) have also been isolated (particularly with Yb and Sm), for instance, with a terbutylated pyrazolate. 182 Generally speaking, interest for 4f-4f polymetallic species mainly lies, in addition to improved catalytic efficiency, in the fine-tuning of magnetic and spectroscopic properties as well as in the design of precursors for lanthanide-based materials.…”

Structures of Rare Earth Homodinuclear Macrocyclic Complexes with the Polyamine Polycarboxylic Ligand 1,4,7,10,14,17,20,23-Octaazacyclohexacosane-1,4,7,10,14,17,20,23-octaacetic Acid (H8OHEC) in the Crystal and in Solution

“…This is supported by the protonation scheme of H 8 OHEC established by potentiometric Figure 1a. Solid-state conformation of 1 with numbering scheme; titration and pH-dependent 1 [10] In neutral or acidic solution, the lanthanide ions are coordinated only weakly to the outer sphere of the cyclic ligand [13] and free lanthanide ions can be detected electrochemically, [14] by 89 Y-NMR, [9] and by reaction with xylenol orange.…”