Synthesis, Potentiometry, and NMR Studies of Two New 1,7-Disubstituted Tetraazacyclododecanes and Their Complexes Formed with Lanthanide, Alkaline Earth Metal, Mn2+, and Zn2+ Ions

Laszlo Burai, Jimin Ren, Zoltan Kovacs, Erno Brücher, A. Dean Sherry

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Abstract

Two new 1,7-disubstituted-1,4,7,10-tetraazacyclododecane ligands, DO2P and DO2PME, and their complexes with Mg2+, Ca2+, Sr2+, Mn2+, Zn2+ and Ln3+ were prepared and characterized by pH potentiometry. The pH titration data showed that DO2P and DO2PME both form 1:1 M:L complexes with all divalent and trivalent metal ions. Protonated complexes did not appear to form with the bis(phosphonate ester) ligand, DO2PME, but were evident for all of the metal ion-DO2P complexes. The alkaline earth metal ion-DO2P complexes formed both ML and MHL complexes while the lanthanide ion (Ln3+), Zn2+, and Mn2+ complexes of DO2P formed ML, MHL, and MH2L species. Zn2+ formed the most stable complex with both ligands. The stability (β101) of the LnDO2PME+ complexes increased by about 2 orders of magnitude along the lanthanide series (La3+ to Lu3+) while the stability of the LnDO2P- complexes over this same series increased by over 3 orders of magnitude. The bis(phosphonate) ligand, DO2P, and some of its complexes formed with Ln3+ ions were further examined by NMR spectroscopy. 1H and 31P spectra of DO2P collected as a function of pH provided evidence that the first two protonations on the ligand take place largely at the tertiary nitrogens. The similarity of the 31P chemical shifts of EuDO2P- and EuDOTP5- indicate that DO2P forms an "in-cage" complex with Eu3+ using all four macrocyclic ring nitrogens and the two phosphonate sidearms as ligands. 17O NMR shifts of the water signal indicated that the DyDO2P- complex has two inner-sphere coordinated water molecules. In the presence of excess of DO2P, a 1:2 metal:ligand, LnDO2P(HDO2P)4-, complex forms with the second ligand interacting only weakly with the coordination sites left vacant by the first DO2P. Both water proton relaxivity data for GdDO2P- and 31P NMR spectra of EuDO2P- provide evidence for formation of an "out-of-cage" LnH2DO2P+ complex at low pH values (<6.5) in which the two phosphonate groups of DO2P are only involved in bonding with the lanthanide cation.

Original languageEnglish (US)
Pages (from-to)69-75
Number of pages7
JournalInorganic Chemistry
Volume37
Issue number1
StatePublished - Jan 12 1998

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Alkaline Earth Metals
potentiometric analysis
Lanthanoid Series Elements
alkaline earth metals
Nuclear magnetic resonance
Ions
Ligands
Organophosphonates
nuclear magnetic resonance
ligands
synthesis
ions
Metal ions
metal ions
Water
Nitrogen
water
trivalent ions
nitrogen
Protonation

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

@article{63d6122f70b247e588525c8a3e420817,
title = "Synthesis, Potentiometry, and NMR Studies of Two New 1,7-Disubstituted Tetraazacyclododecanes and Their Complexes Formed with Lanthanide, Alkaline Earth Metal, Mn2+, and Zn2+ Ions⊥",
abstract = "Two new 1,7-disubstituted-1,4,7,10-tetraazacyclododecane ligands, DO2P and DO2PME, and their complexes with Mg2+, Ca2+, Sr2+, Mn2+, Zn2+ and Ln3+ were prepared and characterized by pH potentiometry. The pH titration data showed that DO2P and DO2PME both form 1:1 M:L complexes with all divalent and trivalent metal ions. Protonated complexes did not appear to form with the bis(phosphonate ester) ligand, DO2PME, but were evident for all of the metal ion-DO2P complexes. The alkaline earth metal ion-DO2P complexes formed both ML and MHL complexes while the lanthanide ion (Ln3+), Zn2+, and Mn2+ complexes of DO2P formed ML, MHL, and MH2L species. Zn2+ formed the most stable complex with both ligands. The stability (β101) of the LnDO2PME+ complexes increased by about 2 orders of magnitude along the lanthanide series (La3+ to Lu3+) while the stability of the LnDO2P- complexes over this same series increased by over 3 orders of magnitude. The bis(phosphonate) ligand, DO2P, and some of its complexes formed with Ln3+ ions were further examined by NMR spectroscopy. 1H and 31P spectra of DO2P collected as a function of pH provided evidence that the first two protonations on the ligand take place largely at the tertiary nitrogens. The similarity of the 31P chemical shifts of EuDO2P- and EuDOTP5- indicate that DO2P forms an {"}in-cage{"} complex with Eu3+ using all four macrocyclic ring nitrogens and the two phosphonate sidearms as ligands. 17O NMR shifts of the water signal indicated that the DyDO2P- complex has two inner-sphere coordinated water molecules. In the presence of excess of DO2P, a 1:2 metal:ligand, LnDO2P(HDO2P)4-, complex forms with the second ligand interacting only weakly with the coordination sites left vacant by the first DO2P. Both water proton relaxivity data for GdDO2P- and 31P NMR spectra of EuDO2P- provide evidence for formation of an {"}out-of-cage{"} LnH2DO2P+ complex at low pH values (<6.5) in which the two phosphonate groups of DO2P are only involved in bonding with the lanthanide cation.",
author = "Laszlo Burai and Jimin Ren and Zoltan Kovacs and Erno Br{\"u}cher and Sherry, {A. Dean}",
year = "1998",
month = "1",
day = "12",
language = "English (US)",
volume = "37",
pages = "69--75",
journal = "Inorganic Chemistry",
issn = "0020-1669",
publisher = "American Chemical Society",
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TY - JOUR

T1 - Synthesis, Potentiometry, and NMR Studies of Two New 1,7-Disubstituted Tetraazacyclododecanes and Their Complexes Formed with Lanthanide, Alkaline Earth Metal, Mn2+, and Zn2+ Ions⊥

AU - Burai, Laszlo

AU - Ren, Jimin

AU - Kovacs, Zoltan

AU - Brücher, Erno

AU - Sherry, A. Dean

PY - 1998/1/12

Y1 - 1998/1/12

N2 - Two new 1,7-disubstituted-1,4,7,10-tetraazacyclododecane ligands, DO2P and DO2PME, and their complexes with Mg2+, Ca2+, Sr2+, Mn2+, Zn2+ and Ln3+ were prepared and characterized by pH potentiometry. The pH titration data showed that DO2P and DO2PME both form 1:1 M:L complexes with all divalent and trivalent metal ions. Protonated complexes did not appear to form with the bis(phosphonate ester) ligand, DO2PME, but were evident for all of the metal ion-DO2P complexes. The alkaline earth metal ion-DO2P complexes formed both ML and MHL complexes while the lanthanide ion (Ln3+), Zn2+, and Mn2+ complexes of DO2P formed ML, MHL, and MH2L species. Zn2+ formed the most stable complex with both ligands. The stability (β101) of the LnDO2PME+ complexes increased by about 2 orders of magnitude along the lanthanide series (La3+ to Lu3+) while the stability of the LnDO2P- complexes over this same series increased by over 3 orders of magnitude. The bis(phosphonate) ligand, DO2P, and some of its complexes formed with Ln3+ ions were further examined by NMR spectroscopy. 1H and 31P spectra of DO2P collected as a function of pH provided evidence that the first two protonations on the ligand take place largely at the tertiary nitrogens. The similarity of the 31P chemical shifts of EuDO2P- and EuDOTP5- indicate that DO2P forms an "in-cage" complex with Eu3+ using all four macrocyclic ring nitrogens and the two phosphonate sidearms as ligands. 17O NMR shifts of the water signal indicated that the DyDO2P- complex has two inner-sphere coordinated water molecules. In the presence of excess of DO2P, a 1:2 metal:ligand, LnDO2P(HDO2P)4-, complex forms with the second ligand interacting only weakly with the coordination sites left vacant by the first DO2P. Both water proton relaxivity data for GdDO2P- and 31P NMR spectra of EuDO2P- provide evidence for formation of an "out-of-cage" LnH2DO2P+ complex at low pH values (<6.5) in which the two phosphonate groups of DO2P are only involved in bonding with the lanthanide cation.

AB - Two new 1,7-disubstituted-1,4,7,10-tetraazacyclododecane ligands, DO2P and DO2PME, and their complexes with Mg2+, Ca2+, Sr2+, Mn2+, Zn2+ and Ln3+ were prepared and characterized by pH potentiometry. The pH titration data showed that DO2P and DO2PME both form 1:1 M:L complexes with all divalent and trivalent metal ions. Protonated complexes did not appear to form with the bis(phosphonate ester) ligand, DO2PME, but were evident for all of the metal ion-DO2P complexes. The alkaline earth metal ion-DO2P complexes formed both ML and MHL complexes while the lanthanide ion (Ln3+), Zn2+, and Mn2+ complexes of DO2P formed ML, MHL, and MH2L species. Zn2+ formed the most stable complex with both ligands. The stability (β101) of the LnDO2PME+ complexes increased by about 2 orders of magnitude along the lanthanide series (La3+ to Lu3+) while the stability of the LnDO2P- complexes over this same series increased by over 3 orders of magnitude. The bis(phosphonate) ligand, DO2P, and some of its complexes formed with Ln3+ ions were further examined by NMR spectroscopy. 1H and 31P spectra of DO2P collected as a function of pH provided evidence that the first two protonations on the ligand take place largely at the tertiary nitrogens. The similarity of the 31P chemical shifts of EuDO2P- and EuDOTP5- indicate that DO2P forms an "in-cage" complex with Eu3+ using all four macrocyclic ring nitrogens and the two phosphonate sidearms as ligands. 17O NMR shifts of the water signal indicated that the DyDO2P- complex has two inner-sphere coordinated water molecules. In the presence of excess of DO2P, a 1:2 metal:ligand, LnDO2P(HDO2P)4-, complex forms with the second ligand interacting only weakly with the coordination sites left vacant by the first DO2P. Both water proton relaxivity data for GdDO2P- and 31P NMR spectra of EuDO2P- provide evidence for formation of an "out-of-cage" LnH2DO2P+ complex at low pH values (<6.5) in which the two phosphonate groups of DO2P are only involved in bonding with the lanthanide cation.

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VL - 37

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EP - 75

JO - Inorganic Chemistry

JF - Inorganic Chemistry

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