Lanthanide(III) Complexes of Tripodal N-Donor Ligands:  Structural Models for the Species Involved in Solvent Extraction of Actinides(III)

Abstract

The complexation of lanthanides(III) by the tripodal ligands tpa (tris[(2-pyridyl)methyl]amine) and tpza (tris[(2-pyrazinyl)methyl]amine) has been investigated by solution NMR studies and by X-ray crystallography. The crystallographic studies show that both tpa and the new ligand tpza form complexes with a 1:1 metal:ligand ratio in which the tripodal amine acts as a tetradentate ligand. For the tpa complexes the remaining coordination sites are occupied by chloride counterions to give 7-coordination (Eu, Tb, Lu) or by chloride counterions and a methanol molecule to give 8-coordination (Nd). In [Nd(tpza)(H(2)O)(3)(CH(3)CN)(3)](ClO(4))(3).3H(2)O the remaining coordination sites are occupied by water and acetonitrile molecules to give 10-coordination while the perchlorate counterions remain non coordinating. Tpza complexes have been isolated from acetonitrile solution and dissociate completely in methanol, while the complexes of the more basic tpa can be isolated from methanol and exist in water in equilibrium with the free ligand. Solvent extraction studies of lanthanides(III) and actinides(III) from nitric acid solutions show that the new ligand tpza is, unlike tpa, a selective complexant of actinides(III). Considering their structural analogy, this difference could be explained in terms of the electronic differences between the two ligands resulting in a stronger affinity of actinides(III) for the softer donor tpza.

Effect of counter-anions on the adsorption of trivalent actinides and lanthanides on tertiary pyridine resin in alcoholic chloride and nitrate solutions

“…Pyridine groups generally coordinate to metal cations by using N-atoms and they are categorized as soft-donor type ligands [14]. It has been reported that pyridine-type N-donor ligands can selectively extract trivalent An from Ln [12,13], suggesting that the pyridine groups have a larger affinity for An than for Ln(III) [15]. On the other hand, trivalent An and Ln cations are tightly hydrated with 8-9 water molecules in aqueous solution [16][17][18][19].…”

Structure, Stability, Dynamics, High‐Field Relaxivity and Ternary‐Complex Formation of a New Tris(aquo) Gadolinium Complex

“…[31] The three arms of the dpaa ligand adopt a pincer-like arrangement around the metal centre, whereas the three picolinate arms adopt a helical arrangement in the tpaa 3À complex. This behaviour does not lead to significant differences in the Lu À O carboxy bond length (mean values: 2.27(2) and 2.30(4) in LuA C H T U N G T R E N N U N G (dpaa) and LuA C H T U N G T R E N N U N G (tpaa), respectively) and the Lu À N bond length (mean values: 2.46(1) and 2.48 (9) in LuA C H T U N G T R E N N U N G (dpaa) and LuA C H T U N G T R E N N U N G (tpaa), respectively).…”

“…The compositions of the studied solutions and relaxivity values are reported in the Supporting Information. The theoretical expressions given by Equation (33) of the mean relaxivities r 1 and r 2 , derived in the Theory section, with the equilibrium concentration [C] eq of the free complex given by Equation (31), were fitted to their experimental counterparts. The theoretical mean relaxivities r 1 and r 2 are displayed in Figure 6 for selected values of n BSA = 2, 4, 10 and 20 and associated formation constants per site k = 1300, 360, 110 and 50 L mol À1 , which are compatible with the experimental value of q .…”

Effective modulation of lanthanide luminescence functions via stereo-controlled ligand synthesis: Effects of ligand chirality on lanthanide anion sensing

“…They also form stable lanthanide complexes exhibiting characteristic luminescence properties [8][9][10][11]. Mazzanti and co-workers determined the crystal structure of EuCl 3 complex with parent tris(2-pyridylmethyl)amine 5, in which three Cl − anions directly coordinated with the Eu 3+ center together with four nitrogen atoms of the ligand [8]. A few chiral versions of tris(2-pyridylmethyl)amine have recently been reported.…”

“…Mazzanti and co-workers characterized 1:1 complexes between tripode 5 and some lanthanide chlorides [8]. Their X-ray crystallographic studies revealed that four nitrogen atoms effectively coordinated with the lanthanide cation.…”