The formation of ion-pair adducts between the cationic complex La(THP)3+ (THP = 1,4,7,10-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane) and the anionic complexes Tm(DOTA)- (DOTA = 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetate), Tm(DTPA)2- (DTPA = diethylenetriamine-N,N,N',N",N"-pentaacetate), Tm(TTHA)3- (TTHA = triethylenetetraamine-N,N,N',N",N"',N"'-hexaacetate), and Tm(DOTP)5- (DOTP = 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetrakis(methylenephosphonate)) is examined by 13C NMR spectroscopy. The induced 13C shifts of the La(THP)3+ complex are followed by titration of the Tm(III) complexes of DOTA, DTPA, and TTHA at pH 7. From these data, the stability constants are calculated to be beta 1 = 64 M-1 (1:1), beta 1 = 296 M-1 (1:1), and beta 2 = 26,000 M-2 (2:1) for the ion pairs of La(THP)3+, with Tm(DOTA)-, Tm(DTPA)2-, and Tm(TTHA)3-, respectively. The La(THP)3+,Tm(DOTP)5- system elicits chiral resolution of the rapidly interconverting Tm(DOTP)5- isomers.

The lanthanide coordination of the macrocyclic ligands cy(DTPA-EN) and cy(DTPA-EN-DTPA-EN) was studied in aqueous solution. 17O NMR measurements on the DyIII complexes showed that, in both complexes, the first coordination sphere of the LnIII ion contains one water molecule, leaving eight coordination sites for the ligand molecule. 89Y and 139La NMR analysis confirmed that the coordination mode of cy(DTPA-EN-DTPA-EN) is similar to that of the acyclic DTPA-bis(amide) derivatives. However, as a result of the cyclic nature of the ligands considered, the number of isomers in solution is lower than for the acyclic compounds. From variable-temperature 1H and 13C NMR data, we conclude that, in the respective LnIII complexes in solution, the cy(DTPA-EN) ligand is present in two rapidly interconverting isomers, whereas the cy(DTPA-EN-DTPA-EN) ligand exists in four isomeric forms. Two types of exchange processes are observed for the cy(DTPA-EN-DTPA-EN) complexes; one is fast on the NMR time scale and does not require decoordination of the ligand, and the second is relatively slow and decoordination is necessary to realize the interconversion. The complexes of cy(DTPA-EN) and the lighter LnIII ions (Ln = La → Eu) precipitated, probably due to the formation of binuclear complexes. Comparisons are made with the previously studied acyclic DTPA-bis(amides).

The structures of Dy(CF3SO3)3 in water, methanol, and 2-propanol have been investigated with the use of multinuclear NMR techniques. Dy(III)-induced 17O NMR shifts of the solvent afforded estimates of the average number of inner-sphere solvent molecules. Information on the location of the triflate anion was obtained by longitudinal 19F relaxation rates. The data suggest that the predominant species in the various solvents are [Dy(H2O)8][CF3SO3]3, [Dy(CF3SO3)1 - 2(CH3OH)6][CF3SO3], and Dy(CF3SO3)3(i-PrOH)3. Upon addition of water to solutions of Dy(CF3SO3)3 in anhydrous organic solutions the solvent molecules and the triflate anions are expelled from the first coordination sphere of Dy(III) simultaneously.