Stability, relaxometric and computational studies on Mn2+ complexes with ligands containing a cyclobutane scaffold

摘要: The stability constants of Mn2+ complexes with ligands containing a trans-1,2-cyclobutanediamine spacer functionalized picolinate and/or carboxylate functions were determined using potentiometric titrations (25 °C, 0.1 M KCl). constant the complex hexadentate ligand four acetate groups (L14−, log KMnL = 10.26) is improved upon replacing one (L24−, 14.71) or two (L34−, 15.81) picolinates. [Mn(L1)]2− contains water molecule coordinated to metal ion in aqueous solutions, as evidenced by 1H NMRD studies and 17O chemical shifts transverse relaxation rates. relaxivities at 60 MHz (3.3 2.4 mM−1 s−1 25 37 respectively) are comparable those monohydrated such [Mn(edta)]2−. exchange rate inner-sphere (k298ex 248 × 106 s−1) slightly lower than that edta4− analogue. DFT calculations (M11/def2-TZVP) suggest reaction follows dissociatively activated mechanism, providing activation parameters reasonably good agreement experimental data. also show hyperfine coupling A/ℏ affected changes Mn–Owater distance orientation respect Mn–O vector.