Authors
Anwita Roy, Deepak Krishnan Balaji, Joseph A Spernyak, Janet R Morrow
Published in
Inorganic chemistry. Jun 15, 2026. Epub Jun 15, 2026.
Abstract
Three pentadentate ligands based on 1,4,7-triazacyclononane (TACN) bearing 6-methyl-2-picolyl pendants and ancillary groups alkyl-sulfonate (L1), benzyl (L2), or proton (L3) were prepared to generate Fe(II) and Co(II) complexes as paramagnetic shift (parashift) agents with available coordination sites for anion binding. The solid-state structure of [Co(L2)(NO3)](NO3) confirms a six-coordinate complex cation with distorted octahedral geometry. 17O NMR spectroscopy studies support rapidly exchanging inner-sphere water for [Co(L1)]+, [Co(L2)]2+, and [Co(L3)]2+ at neutral pH and for [Fe(L1)]+ and [Fe(L2)]2+ under mildly acidic conditions. The methyl proton resonances of [Co(L1)]+ and [Co(L2)]2+ appear at -45 ppm and +40 ppm and those of [Co(L3)]2+ appear at -51 ppm and +21 ppm, compared to those of the symmetrical complex [Co(L4)]2+ at 8 ppm. [Fe(L1)]+ and [Fe(L2)]2+ have methyl proton resonances at -38 or -39 ppm, which compare to that of [Fe(L4)]2+ at 21 ppm. 1H and 19F NMR spectroscopy studies suggest fluoride binds as an inner-sphere ligand to Fe(II) complexes and to [Co(L1)]+ and [Co(L2)]2+. Co(II) and Fe(II) complexes with bound water show second-sphere interactions with trifluorolactate and fluoride as supported by NMR studies. Magnetic resonance spectroscopy imaging at 7 T demonstrates strong, well-resolved methyl signals for [Co(L1)]+ and [Co(L2)]2+, highlighting their potential as parashift probes.
PMID:
42295842
Bibliographic data and abstract were imported from PubMed on 15 Jun 2026.
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