Synthesis, crystal structures and NMR and luminescence spectra of lanthanide complexes of 1,4,7,10-tetraazacyclododecane with N-methylene(phenyl)phosphinic acid pendant arms †

Abstract

Complexes of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayltetramethylenetetrakis(phenylphosphinic acid) H 4 L 1 with yttrium and a number of lanthanides were synthesized and the crystal structures of Li[LaLThe complexes are isostructural with RSRS configurations at the phosphorus atoms. The ligand is co-ordinated by four nitrogen atoms in a plane and by four phosphinate oxygen atoms in a parallel plane. The planes form a twisted square prismatic co-ordination sphere. A molecule of water capping the O 4 plane completes the co-ordination sphere of both ions. Solution properties of the complexes were investigated by 1 H and 31 P NMR. In solution six possible isomers with different configurations on phosphorus atoms are in equilibrium. The most abundant shows the RRRS configuration. A dynamic behavior similar to lanthanide complexes of 1,4,7,10tetraazacyclododecane-1,4,7,10-tetraacetic acid is not observed. The NMR as well as luminescence measurements show that no water molecule is co-ordinated directly to the lanthanide ions in solution. The ions Li ϩ and Na ϩ form stable ion pairs with the complexes in methanol-d 4 solution as confirmed by the lanthanide induced shift of 7 Li and 23 Na resonances in the presence of paramagnetic lanthanide ions. The ion pairs are not stable in aqueous solution. The alkali metal ion is located close to fourfold magnetic axes of the complexes above the oxygen atoms and between the phenyl rings. Luminescence spectra of [LnL 1 ] Ϫ , Ln = Eu or Tb, indicate low symmetry of the species and coordination number 8.

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

“…Taking into account also the luminescence measurements on europiA C H T U N G T R E N N U N G um-A C H T U N G T R E N N U N G (III) complexes of tetraphosphorus acid 1,4,7,10-tetraazacyclododecane (cyclen) derivatives in which a strong secondsphere hydration of the complexes was proven [18] and the precision of the above luminescence measurements, it can be concluded that the final product of Eu III complexation has no coordinated water molecule. It also agrees with the previous 17 O NMR spectroscopic measurements.…”

“…[13,[16][17][18]21,22] Similarly, in the solid state, both SA and TSA structures were observed for the complexes of dota-like ligands [3,6,9] and only the TSA arrangement was found in the complexes of dotp and other tetraphosphorus derivatives. [13,[16][17][18]21,22] Dota complexes are nona-coordinated and have one water molecule capping the O 4 -plane, except for the TSA isomer of the Yb 3 + and Lu 3 + complexes, which have no inner-sphere water. [20a] In contrast, the coordinated water molecule is missing (except the largest lanthanideA C H T U N G T R E N N U N G (III) ions) in the complexes of tetraphosphorus ligands.…”

“…[27] The phenylphosphinate complexes, [LnA C H T U N G T R E N N U N G (dotp Ph , see Scheme 1), present in solution as a mixture of the six possible isomers with R or S orientations at the P atoms, did not show such a break and, thus, were considered to be isostructural, with hydration number q = 0 all along the lanthanide series. [17] However, these conclusions must be taken with care. It has recently been shown for the predominant RRRR (SSSS) solution isomer of the several Ln III tetraazaphosphinate and tetraazaphosphonate complexes across the lanthanide series, as well as for the [LnA C H T U N G T R E N N U N G (dotp)] 5À complexes, that the positions of the breaks observed in the plots of the 17 O water LIS values, which directly reflect the change of inner-sphere water coordination (q value), do not correspond with those observed for the 31 P LIS data.…”

“…[17] However, these conclusions must be taken with care. It has recently been shown for the predominant RRRR (SSSS) solution isomer of the several Ln III tetraazaphosphinate and tetraazaphosphonate complexes across the lanthanide series, as well as for the [LnA C H T U N G T R E N N U N G (dotp)] 5À complexes, that the positions of the breaks observed in the plots of the 17 O water LIS values, which directly reflect the change of inner-sphere water coordination (q value), do not correspond with those observed for the 31 P LIS data. [18,22] The breaks of the 17 O LIS plots occur at the beginning of the Ln series, which corresponds to a change of q = 1 for the Ce III complexes to q = 0 for the rest of the series.…”

“…As the Ce III ion has the largest ionic radius, it is able to form nona-coordinated complexes (with an apical inner-sphere water molecule) even with tetrakis(methyl- phosphorus acid) cyclen derivatives. [17] The ceriumA C H T U N G T R E N N U N G (III) complex is harder to protonate to get kinetically important triprotonated species; it leads to a lower log K 311 value. But once the complex is protonated it decomposes faster than the other ones ( d k 1 in Table 6), possibly due to a better exposure of the central ion to solvent.…”