An unusual nitroso⋯nitroso interaction in the coordination polymer structures of Ni(ii) and Co(ii) complexes with the α,ω-bis(benzotriazoloxy)alkane system

Abstract

A novel type of NO⋯NO supramolecular interaction is reported for the first time. Three new polymeric coordination complexes, two nickel(II) complexes, {[Ni(μ-L¹)₂(NCS)₂]}_n, (1) {[Ni(μ-L²)₂(NCS)₂]}_n, (2) and a cobalt(II) complex {[Co(μ-L³)₂(NCS)₂]}_n (3) have been synthesized with the organic ligand α,ω-bis(benzotriazoloxy)alkane (L¹ = 1,3-bis(benzotriazol-1-yl)-1,3-dioxapropane; L² = 1,5-bis (benzotriazol-1-yl)-1,5-dioxapentane; L³ = 1,6-bis(benzotriazol-1-yl)-1,6-dioxahexane) and thiocyanate as counterions. The complexes were characterized by various physical measurements such as elemental analysis, FT-IR, UV–Vis, NMR and mass spectroscopy. The single crystal X-ray analysis revealed that complexes 1 and 2 have a 1D coordination polymer helical structure whereas complex 3 has a 2D polymer anti corrugate structure. Complexes 2 and 3 were found to be involved in packing in the crystal structures by a very unusual anti-parallel strong NO⋯NO interaction. In addition, the π-acidity of the triazole ring moiety increased upon the coordination of the Ni ion which led to the establishment of lone pair–π (lp–π) interactions. Moreover, all of the complexes show different intermolecular interactions (H-bonds, π–π, lone pair–π and anti-parallel NO⋯NO) whose energetics and role in the crystal packing have been evaluated with theoretical DFT calculations.