Ligand-dictated planar versus bent nickel(II) chelates of the Schiff bases: Synthesis, crystal structures, optical properties, DFT and molecular docking studies

Abstract

Two nickel(II) coordination compounds [Ni(LI)2] (1) and [Ni(LII)2] (2) (HLI = N-cyclohexyl-3-methoxysalicylideneimine, HLII = N-cyclohexyl-3-ethoxysalicylideneimine) were synthesized with the aim to reveal and compare the influence of the electronically and structurally similar methyl (Me) and ethyl (Et) funcionalities in a close proximity to the chelate backbone of the corresponding parent ligand. It was established that a minor difference in the structure of the parent ligand (Me in LI vs. Et in LII) leads to a crucial difference in the geometry of a complex molecule: a planar structure of 1 with two cycloalkane functionalities directed on the opposite sides of a molecule, and a bent structure of 2 with two cycloalkane functionalities directed on the convex side of a molecule. The coordination core of both complexes is a NiN2O2 planar square, formed due to two trans-coordinated ligands LI and LII, respectively. Solutions of the title compounds in CH2Cl2, MeOH and EtOH absorb up to about 475 nm due to intraligand transitions and LMCT. The DFT-based calculations were also applied to shed light on the structural and optical features of 1 and 2. In silico prediction using a molecular docking approach showed that both complexes can potentially inhibit a number of the SARS-CoV-2 proteins. The so-called ligand efficiency scores for complex Nsp14_N7-MTase–1 are within the recommended ranges for a drug, while the same scores for complexes Nsp14_N7-MTase–2, PLpro–1 and Mpro–1 fall in the ranges for a Hit.