Alkaline Earth Metal and Lanthanide(III) Complexes of Ligands Based upon 1,4,7,10-Tetraazacyclododecane-1,7-bis(acetic acid)

Jurriaan Huskens, Diego A. Torres, Zoltan Kovacs, João P. André, Carlos F G C Geraldes, A. Dean Sherry

Research output: Contribution to journalArticle

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Abstract

The macrocyclic ligand DO2A (1,4,7,10-tetraazacyclododecane-1,7-bis(acetic acid)) was prepared and used as a building block for four new macrocyclic ligands having mixed side-chain chelating groups. These ligands and their complexes with MgII, CaII, and LnIII were studied extensively by potentiometry, high-resolution NMR, and water proton relaxivity measurements. The protonation constants of all compounds compared well with those of other cyclen-based macrocyclic ligands. All CaII complexes were found to be more stable than the corresponding MgII complexes. Trends for the stabilities of the LnIII complexes are discussed and compared with literature data, incorporating the effects of water coordination numbers, LnIII contraction, and the nature of the side chains and the steric hindrance between them. 1H NMR titrations of DO2A revealed that the first and second protonations take place preferentially at the secondary ring nitrogens, while the third and fourth involved protonation of the acetates. 17O NMR shifts showed that the DyDO2A+ complex had two inner-sphere water molecules. Water proton spin - lattice relaxation rates for the GdDO2A+ complex were also consistent with water exchange between bulk water and two inner-sphere GdIII coordination positions. Upon formation of the diamagnetic complexes of DO2A (CaII, MgII, LaIII, and LuIII), all of the macrocyclic ring protons became nonequivalent due to slow confortnational rearrangements, while the signals for the acetate CH2 protons remained a singlet.

Original languageEnglish (US)
Pages (from-to)1495-1503
Number of pages9
JournalInorganic Chemistry
Volume36
Issue number7
StatePublished - Mar 26 1997

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Alkaline Earth Metals
Lanthanoid Series Elements
alkaline earth metals
acetic acid
Acetic Acid
Ligands
ligands
Protons
Water
Protonation
water
protons
Nuclear magnetic resonance
nuclear magnetic resonance
acetates
Acetates
potentiometric analysis
Spin-lattice relaxation
rings
Chelation

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

Alkaline Earth Metal and Lanthanide(III) Complexes of Ligands Based upon 1,4,7,10-Tetraazacyclododecane-1,7-bis(acetic acid). / Huskens, Jurriaan; Torres, Diego A.; Kovacs, Zoltan; André, João P.; Geraldes, Carlos F G C; Sherry, A. Dean.

In: Inorganic Chemistry, Vol. 36, No. 7, 26.03.1997, p. 1495-1503.

Research output: Contribution to journalArticle

Huskens, Jurriaan ; Torres, Diego A. ; Kovacs, Zoltan ; André, João P. ; Geraldes, Carlos F G C ; Sherry, A. Dean. / Alkaline Earth Metal and Lanthanide(III) Complexes of Ligands Based upon 1,4,7,10-Tetraazacyclododecane-1,7-bis(acetic acid). In: Inorganic Chemistry. 1997 ; Vol. 36, No. 7. pp. 1495-1503.
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abstract = "The macrocyclic ligand DO2A (1,4,7,10-tetraazacyclododecane-1,7-bis(acetic acid)) was prepared and used as a building block for four new macrocyclic ligands having mixed side-chain chelating groups. These ligands and their complexes with MgII, CaII, and LnIII were studied extensively by potentiometry, high-resolution NMR, and water proton relaxivity measurements. The protonation constants of all compounds compared well with those of other cyclen-based macrocyclic ligands. All CaII complexes were found to be more stable than the corresponding MgII complexes. Trends for the stabilities of the LnIII complexes are discussed and compared with literature data, incorporating the effects of water coordination numbers, LnIII contraction, and the nature of the side chains and the steric hindrance between them. 1H NMR titrations of DO2A revealed that the first and second protonations take place preferentially at the secondary ring nitrogens, while the third and fourth involved protonation of the acetates. 17O NMR shifts showed that the DyDO2A+ complex had two inner-sphere water molecules. Water proton spin - lattice relaxation rates for the GdDO2A+ complex were also consistent with water exchange between bulk water and two inner-sphere GdIII coordination positions. Upon formation of the diamagnetic complexes of DO2A (CaII, MgII, LaIII, and LuIII), all of the macrocyclic ring protons became nonequivalent due to slow confortnational rearrangements, while the signals for the acetate CH2 protons remained a singlet.",
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N2 - The macrocyclic ligand DO2A (1,4,7,10-tetraazacyclododecane-1,7-bis(acetic acid)) was prepared and used as a building block for four new macrocyclic ligands having mixed side-chain chelating groups. These ligands and their complexes with MgII, CaII, and LnIII were studied extensively by potentiometry, high-resolution NMR, and water proton relaxivity measurements. The protonation constants of all compounds compared well with those of other cyclen-based macrocyclic ligands. All CaII complexes were found to be more stable than the corresponding MgII complexes. Trends for the stabilities of the LnIII complexes are discussed and compared with literature data, incorporating the effects of water coordination numbers, LnIII contraction, and the nature of the side chains and the steric hindrance between them. 1H NMR titrations of DO2A revealed that the first and second protonations take place preferentially at the secondary ring nitrogens, while the third and fourth involved protonation of the acetates. 17O NMR shifts showed that the DyDO2A+ complex had two inner-sphere water molecules. Water proton spin - lattice relaxation rates for the GdDO2A+ complex were also consistent with water exchange between bulk water and two inner-sphere GdIII coordination positions. Upon formation of the diamagnetic complexes of DO2A (CaII, MgII, LaIII, and LuIII), all of the macrocyclic ring protons became nonequivalent due to slow confortnational rearrangements, while the signals for the acetate CH2 protons remained a singlet.

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