Experimental and computational studies on pseudotetrahedral nickel(ii)-(S or R)-dihalogen-salicylaldiminates with Δ- or Λ-chirality induction at-metal

In this study, three pairs of pseudotetrahedral C2-symmetrical bis[(S or R)-N-1-(phenyl)ethyl-(2,4-X1,X2-salicylaldiminato-κ2N,O)]-Δ/Λ-nickel(II), Δ/Λ-NiSL1–3 or Λ/Δ-NiRL1–3 (X1, X2 = Cl, Cl; Br, Br; Cl, Br) with Δ- or Λ-chirality induction at-metal were synthesized, respectively. X-ray molecular structures showed the formation of a N2O2-chromophore around nickel(II) from two molecules of Schiff bases in a pseudotetrahedral geometry. The structural analysis further suggested the isolation of opposite configured Δ-Ni and Λ-Ni diastereomers for S- and R-HL1–3 Schiff base ligands in an enantiopure crystal, resulting from diastereoselection and chirality induction at-metal. The gas-phase optimized structures for Δ-NiSL1–3 or Λ-NiRL1–3 are also slightly more stable by 0.10–1.70 kcal mol−1. Electronic circular dichroism (ECD) spectra showed expected mirror-image relationships with opposite Cotton effects, confirming the enantiopurity or enantiomeric excess of NiRL1–3 and NiSL1–3 complexes in solutions. Combined analyses of experimental and simulated ECD spectra suggested diastereomeric excess of Δ-NiSL1–3 or Λ-NiRL1–3 in solutions, demonstrating the preservation of chirality induction at-metal alike in solid or gas phases. The analysis of supramolecular packing explored several kinds of intermolecular interactions with the strongest one for halogen⋯oxygen atoms and only halogen at the para-position of salicylaldehyde is involved in these interactions with Br⋯O > Cl⋯O. Hirshfeld surface analysis also supported such kind of interactions at a distance shorter than the sum of the van der Waals radii. The non-covalent interaction (NCI) indices explored the presence of weak attractive interactions resulting from the halogen atoms of the respective structures. The experimental and simulated PXRD patterns revealed a fair matching, confirming the phase purity of bulk crystal samples of these complexes