Mn(II) complexes of novel hexadentate AAZTA-like chelators: a solution thermodynamics and relaxometric study.

摘要: Three novel chelators based on the 6-amino-6-methylperhydro-1,4-diazepine scaffold and possessing three pendant N-acetic or N-α-methylacetic acid have been synthesised. The ligands contain six donor atoms for complexation of MnII ions thus potentially leave an additional site coordination a water molecule. protonation constants stability their complexes formed with ion were determined by pH-potentiometric titrations in 0.15 M NaCl solution at 25 °C compared to those parent AAZTA ligand (AAZTA = tetraacetic acid). In spite similar value total basicity (Σlog K), values MnIIAAZTA-like are more than orders magnitude lower that MnAAZTA (log KMnL 14.19). A detailed 1H 17O NMR relaxometric study was carried out aqueous as function pH, temperature magnetic field strength. NMRD profiles all show shape, typical low-molecular weight systems, but amplitudes markedly differ indicate different degree hydration. behaviour is shown transverse relaxation rates chemical shift data temperature. experimental can be rationalised considering presence mixture two isomeric species differing number (7 6) (1 0) bound molecules. Whereas this type equilibrium has previously reported lanthanide(III) complexes, it observed first time chelates.