Potentiometric and spectroscopic study of copper(II) and nickel(II) complexes of trans-dioxopentaaza macrocycles in aqueous solution

Abstract

The trans-dioxopentaaza macrocycles 2,6-dioxo-1,4,7,10,13-pentaazacyclopentadecane (L 1 ) and 2,6-dioxo-1,4,7,11,14-pentaazacycloheptadecane (L 2 ) have been prepared. Their protonation and metal-binding properties with Cu 2ϩ and Ni 2ϩ have been investigated in 0.10 mol dm Ϫ3 KNO 3 (aq) at 25.0 ЊC by potentiometric pH-metry, calorimetry (in part), electronic absorption and IR spectroscopy. Metal-ion complexation promotes the deprotonation and the co-ordination of the amide nitrogens, resulting in neutral complexes with four nitrogen donors and a MLH Ϫ2 stoichiometry at pH 8. Additional complexes with stoichiometry MHL, ML and MLH Ϫ1 complete the complexation set. The overall stability constants of the complexes were calculated. The electronic spectra support a tetragonal co-ordination of Cu 2ϩ and a square-planar co-ordination of Ni 2ϩ in the MLH Ϫ2 complexes leaving one amino group unco-ordinated. It is suggested that the planar trigonal nature of the coordinated amido nitrogens in trans position to each other in the equatorial plane around Ni 2ϩ or Cu 2ϩ structurally prevents the fifth nitrogen donor from binding at an axial site. The NiL 2 H Ϫ2 complex exhibits a yellow-to-blue conversion equilibrium.

EPR and speciation simulation study of Cu2+ complexes in an amine-based aqueous precursor system used for preparation of superconducting YBCO coatings

“…From the same method, the carbonate content of the strong base which can interfere in further experiments can be calculated. 24…”

Solution chemistry of 1,15-bis(N,N-dimethyl)-5,11-dioxo-8-(N-benzyl)-1,4,8,12,15-pentaazapentadecane with metal ions of biological interest—Insights toward active metal ion containing therapeutics and diagnostic agents

“…et al 14 have recently observed a similar electron withdrawing property of an amide group in the dioxomacrocylic analogues of L a . The benzylamine is also 2-4 log units more basic than the central amine of L 1 -L 4 (Fig.…”

“…However, this behaviour was not observed for the previously studied N,N -bis(2-hydroxyiminopropionyl) propane-1,3-diamine ligand reported 2 by us, nor for dioxocyclomacrocycles, 2,6-dioxo-1,4,7,10,13-pentaazacyclopentadecane and 2,6-dioxo-1,4,7,11,14pentaazacycloheptadecane, investigated by Steenland and coworkers. 14 In contrast to the earlier syntheses of related ligand systems, 7 the compound L a was obtained in a mono-hydrochloride form (C 21 H 38 N 5 O 2 Cl) as a pure diastereoisomer suitable for analysis and potentiometric titrations. The presence of the mono-protonated ligand was revealed by an m/z signal centred at 392.54259 [HL a ] + (C 21 H 38 N 5 O 2 ).…”

Potentiometric and Blood Plasma Simulation Studies of Nickel(II) Complexes of Poly(amino)amido Pentadentate Ligands: Computer Aided Metal-Based Drug Design

“…Jackson et al reported p K a 1 and p K a 2 values for N,N′-bis[aminoethyl] ethanediamne, that is, H 2 N-CH 2 -CH 2 -NH-C(O)-C(O)-NH-CH 2 -CH 2 -NH 2 , (p K a 1 = 9.31 and p K a 2 = 8.43) and N,N′-bis[2-(dimethylamino)-ethyl] ethanediamide, that is, Me 2 N-CH 2 -CH 2 -NH-C(O)-C(O)-NH-CH 2 -CH 2 -NMe 2 , (p K a 1 = 8.72 and p K a 2 = 7.92) [ 12 ]. The low value of the third protonation constant (p K a 3 = log⁡ β 013 − log⁡ β 012 ) of 2.03, 1.74, and 1.98 corresponding to the central pyridyl nitrogen for L1, L2, and L3, respectively, is due to the electronic repulsion effect and the base weakening effect of the adjacent amide groups [ 13 ]. Therefore, it is expected that the protonation constant corresponding to the central pyridyl nitrogen in L1, L2, and L3 should decrease further when two amide groups are present.…”