Synthesis and characterization of Mg(II), Mn(II), Zn(II) and Cd(II) complexes with a new heptaaza Schiff base pendant-armed macrocycle: X-ray crystal structure, NMR and computational study

New 2-aminoethyl pendant-armed Schiff base macrocyclic complexes, [ML7]2+ (M = Mn(II), Mg(II), Zn(II) and Cd(II)), have been prepared via M(II) templated [1 + 1] cyclocondensation of 2,6-diacetylpyridine with a new branched hexamine, N,N,N′,N′-tetrakis(2-aminoethyl)-2,2-dimethylpropane-1,3-diamine. The ligand is a 16-membered pentaaza macrocycle having two 2-aminoethyl pendant arms [L7 is 2,14-dimethyl-6,10-bis(2-aminoethyl)-3,6,10,13,19-pentaazabicyclo[13.3.1]8,8-dimethylnonadeca-1(19),2,13,15,17-pentaene]. The crystal structures of [MnL7]2+ and [MgL7]2+ were determined from X-ray diffraction data. The geometry of the coordination sphere of complexes is a slightly distorted pentagonal bipyramid with the metal ion located within a pentaaza macrocycle and two pendant amines coordinating on opposite sides. All complexes were characterized by IR, microanalysis and except of [MnL7]2+ by 1H NMR, 13C NMR, DEPT135, COSY(H, H) and HMQC spectroscopy. The data indicate that the structure is pentagonal bipyramidal in each case. The structure of all complexes has also been theoretically studied by ab initio Hartree–Fock and density functional theory methods.