Synthesis and crystal structure of the simultaneous binding of Ni(ii) cation and chloride by the protonated 2,4,6 tris-(2-pyridyl)-1,3,5 triazine ligand: theoretical investigations of anion⋯π, π⋯π and hydrogen bonding interactions

Abstract

A new octahedral Ni(II) complex 1 of protonated ligand Htptz⁺ (tptz: 2,4,6-tris(2-pyridyl)-1,3,5-triazine) has been synthesized and characterized by single crystal X-ray analysis. It is noteworthy that the protonated ligand concomitantly chelates the Ni(II) and interacts with two non-coordinated chloride ions via anion⋯π and hydrogen bonding interactions. Moreover, N⁺–H hydrogen bonding occurs with the non-coordinated anion rather than with the coordinated or lattice water molecules. In this work, we demonstrate the role of the protonated ligand and chloride ions in stabilizing the structural integrity through several supramolecular interactions. Besides π⋯π interactions, theoretical investigations provide significant insight about the interplay between anion⋯π and hydrogen bonding interactions that in turn conclusively confirm the decisive role of protonation as well as coordination to the metal center [here Ni(II)]. The different contributions to the complexation energies have been evaluated by using several theoretical models.