Lanthanide(III) Complexes of 4,10‐Bis(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid (trans‐H₆do2a2p) in Solution and in the Solid State: Structural Studies Along the Series

Abstract

Complexes of 4,10-bis(phosphonomethyl)-1,4,7,10-tetraazacyclododecane-1,7-diacetic acid (trans-H(6)do2a2p, H(6)L) with transition metal and lanthanide(III) ions were investigated. The stability constant values of the divalent and trivalent metal-ion complexes are between the corresponding values of H(4)dota and H(8)dotp complexes, as a consequence of the ligand basicity. The solid-state structures of the ligand and of nine lanthanide(III) complexes were determined by X-ray diffraction. All the complexes are present as twisted-square-antiprismatic isomers and their structures can be divided into two series. The first one involves nona-coordinated complexes of the large lanthanide(III) ions (Ce, Nd, Sm) with a coordinated water molecule. In the series of Sm, Eu, Tb, Dy, Er, Yb, the complexes are octa-coordinated only by the ligand donor atoms and their coordination cages are more irregular. The formation kinetics and the acid-assisted dissociation of several Ln(III)-H(6)L complexes were investigated at different temperatures and compared with analogous data for complexes of other dota-like ligands. The [Ce(L)(H(2)O)](3-) complex is the most kinetically inert among complexes of the investigated lanthanide(III) ions (Ce, Eu, Gd, Yb). Among mixed phosphonate-acetate dota analogues, kinetic inertness of the cerium(III) complexes is increased with a higher number of phosphonate arms in the ligand, whereas the opposite is true for europium(III) complexes. According to the (1)H NMR spectroscopic pseudo-contact shifts for the Ce-Eu and Tb-Yb series, the solution structures of the complexes reflect the structures of the [Ce(HL)(H(2)O)](2-) and [Yb(HL)](2-) anions, respectively, found in the solid state. However, these solution NMR spectroscopic studies showed that there is no unambiguous relation between (31)P/(1)H lanthanide-induced shift (LIS) values and coordination of water in the complexes; the values rather express a relative position of the central ions between the N(4) and O(4) planes.

Structure, Dynamics, and Computational Studies of Lanthanide‐Based Contrast Agents

“…The structures of the Ln(trans-DO2A2P) 3− complexes (trans-DO2A2P (Chart 5.10) is the transbisphosphonate analog of DOTA) have been studied by various techniques [313,391,392]. Relaxometric and 17 O NMR studies have shown that the Gd 3+ chelate adopts a TSA coordination geometry, with q = 0 [391].…”

“…Relaxometric and 17 O NMR studies have shown that the Gd 3+ chelate adopts a TSA coordination geometry, with q = 0 [391]. X-ray studies of the DO2A2P complexes along the lanthanide series have shown that the TSA coordination geometry is present for the larger ions (Ln = Ce-Sm), and the TSA for the smaller ones (Ln = Sm-Yb) [392]. PCS shifts for the paramagnetic complexes (except Gd) were rationalized on the basis of the Ce 3+ and Yb 3+ complexes, as models of the TSA and TSA geometries, giving calculated structures in agreement with the solid-sate structures.…”

“…PCS shifts for the paramagnetic complexes (except Gd) were rationalized on the basis of the Ce 3+ and Yb 3+ complexes, as models of the TSA and TSA geometries, giving calculated structures in agreement with the solid-sate structures. Again, breaks observed on plots of 1 H and 31 P PCS data according to Equations (5.14) and (5.15) reflected the change of the relative position of the Ln 3+ ion between the N 4 and O 4 planes of the coordination polyhedron, rather than the change of hydration state of the ion, which is directly reflected by the 17 O contact shifts [392]. Line shape analysis of the 1 H and 13 C NMR spectra of the La 3+ and Lu 3+ complexes versus temperature and DFT calculations were used to study the mechanism of SA /TSA isomerization.…”

A New Tris(phosphonomethyl) Monoacetic Acid Cyclam Derivative: Synthesis, Acid‐Base and Metal Complexation Studies

“…Polyaza macrocycles with appended methylphosphonate groups usually present very high values for the first protonation constant(s), which can hinder the accurate determination of their value(s) by potentiometry, as previously observed. [13,18,[20][21][22][23][24][25][26] This trend has been explained by the effect of spreading the high electron density of the fully deprotonated phosphonate group to the nearest nitrogen atom, [3] or by the formation of strong intramolecular hydrogen bonds. [21] In the case of H 7 te3p1a, the first two protonations have very high values and only an overall constant that corresponds to this double protonation could be determined by the 31 P NMR spectroscopic titration in the alkaline region (pH [9][10][11][12][13][14]; the measurement was performed in an aqueous solution and the ionic strength was maintained at 0.50 mol dm -3 with [N(CH 3 ) 4 ]NO 3 .…”

“…The interpretation of the 31 P NMR spectroscopic chemical shift changes is still mostly empirical as different classes of phosphorus compounds show diverse behaviour. However, a significant amount of data has been published with respect to the aminoalkylphosphonate groups in acyclic [28][29][30][31] and macrocyclic [13,[20][21][22]25,26,[32][33][34][35] compounds. In the 31 P NMR spectroscopic titration of H 7 te3p1a, one of the resonances (δ a ) shows a different pH dependence from those of the other two signals (δ b and δ bЈ ).…”