Pseudotetrahedral Zn(II)-( R or S )-dihalogen-salicylaldiminato complexes with Λ- or Δ-chirality induction at-metal.

Reactions of enantiopure ( S or R )- N -1-(phenyl)ethyl-2,4-X 1 ,X 2 -salicylaldimine ( S -H or R -H; X 1 , X 2 = dihalogen) with Zn(II)-nitrate give bis[( S or R )- N -1-(phenyl)ethyl-2,4-X 1 ,X 2 -salicylaldiminato-κ 2 N,O]-zinc(II), (Δ-Zn S or Λ-Zn R ) with Δ/Λ-chirality induction at-metal in the C 2 -symmetric molecules. EI-mass spectra show parent ion peaks. X-ray structures indicate that two phenolate-oxygen and two imine-nitrogen atoms from two molecules of the Schiff bases coordinate to the Zn(II) ion in a pseudotetrahedral geometry. Structural analyses give evidence that the S - or R -ligand chirality gives only one diastereomer Δ-Zn S or Λ-Zn R in an enantiopure crystal. Gas-phase optimized structures suggest that the Δ-Zn S or Λ-Zn R diastereomers are slightly more stable than Λ-Zn S or Δ-Zn R by 1-2 kcal mol -1 . The intramolecular interactions were analyzed with the Independent Gradient Model (IGM) using the program Multiwfn on the optimized structures and also indicate the diastereomeric preference of Δ-Zn S 1 over Λ-Zn S 1 (or Λ-Zn R 1 over Δ-Zn R 1). Variable time and temperature 1 H NMR spectra support the presence of only one diastereomer Λ-Zn R or Δ-Zn S in the bulk samples, backed by the simulated spectra which exhibit no diastereomerization in solution. In contrast, the reported Zn(II)-( R or S )-salicylaldiminato/naphthaldiminato complexes show a diastereomeric mixture of both Δ- and Λ-forms and a Δ ⇄ Λ equilibrium in solution. Electronic circular dichroism (ECD) spectra in solution display expected mirror-image relationships for the ( S or R )-Schiff base ligands and the ( S or R )-ligated complexes. Combined analyses of experimental and simulated ECD spectra further support the notion of diastereomeric excess of Δ-Zn S or Λ-Zn R in solution. The overall results thus suggest the preservation of chirality at-zinc induced by S - or R -ligands in a solid or solution. Supramolecular packing analyses explore different kinds of intermolecular interactions with the strongest one for X⋯O. Only the halogen atom in the para position is involved in these interactions with Br⋯O > Cl⋯O. Hirshfeld surface analyses also support these interactions between two molecules at a distance shorter than the sum of the vdW radii. Comparison of the experimental and simulated PXRD patterns from the single-crystal X-ray structures shows a good matching and confirms the phase purity of the bulk samples.