A comparative study of noncovalent interactions in various Ni-compounds containing nitrogen heteroaromatic ligands and pseudohalides: A combined experimental and theoretical studies

Abstract

Five mononuclear nickel(II) complexes, [Ni(NCS)2(imz)4] (1) and [Ni(NCS)2(pyz)4] (2), [Ni(NCS)2(3-OHpy)4] (3), [Ni(NCS)2(3-Clpy)4] (4) and [Ni(NCO)2(3-Clpy)2(H2O)2] (5), where imz, pyz, 3-OHpy and 3-Clpy are imidazole, pyrazole, 3-hydroxypyridine and 3-chloropyridine, respectively, have been synthesized and characterized by X-ray crystallographic studies to explore the role of different heteroaromatic ligands and pseudohalides in the crystal packing. The noncovalent interactions witnessed in the crystal packing of these complexes have been well-defined focusing on the recurrent π–stacking motifs, leading to the π–stacked dimeric assemblies. Besides, noncovalent interactions such as, NH(CH)···π, lone pair···π, along with both conventional and nonconventional hydrogen bonding interactions play important roles in the stabilization of these complexes in the solid state. The energetic features of the π–stacking and the importance of additional noncovalent interactions towards cooperatively formed π–stacking dimers were investigated using DFT calculations in combination with the quantum theory of atoms-in-molecules (QTAIM) and noncovalent interaction plot (NCI plot) index computational tools. Remarkably, the aromatic ligands (imidazole, pyridine) through coordination generate favourable antiparallel orientation of the dipoles (180°) in the dimeric form of complexes 1, 3, 4 and 5, and thus exhibit strong π–stacking interaction in comparison to complex 2 (pyrazole) in its dimeric form with the perpendicular orientation of dipoles. This study may provide further insight into elucidating the role of weak noncovalent interactions in the supramolecular assemblies of metal-containing compounds.