Synthesis and characterization of the trans(O6) isomer Ni(II) complex containing symmetrical edta-type ligand with mixed carboxylate and diamine rings: Quantum-mechanical evaluation of different isomers

•The trans(O6) isomer of the [Ni(1,3-pddadp)]2− complex was synthesized and characterized by X-ray structure analysis.•The most probable pathways for formation of trans(O6)-[Ni(1,3-pddadp)]2− anion have been proposed.•QM modeling, B3LYP/TZVP, of different isomers has been done in order to establish their relative stability.•NBO analysis predicts the existence of a 3-center 2-electron (β system) A: -Ni-: B Hyperbonds.•The NBO’s D/A analysis predicts molecular stabilization that comes from charge transfer nA → σNiB* or nB → σNiA*.