Pseudotetrahedral C2-symmetrical Co/Zn(II)-achiral Schiff base complexes with Δ/Λ-chirality induction at-metal as a racemic mixture

• Published in: Journal of molecular structure 2023-11, Vol.1292, p.136078, Article 136078
• Main Authors: Enamullah, Mohammed, Haque, Imdadul, Mim, Afsana, Islam, Mohammad Khairul, Sidhu, Baldeep K., Herbert, David E., Woschko, Dennis, Janiak, Christoph
• Format: Article
• Language: English
• Subjects: Co/Zn(II)-Schiff base complexes; Cyclic voltammetry and thermal analysis; DFT/TD-DFT calculations; X-ray structures; Δ/Λ-chirality induction at-metal
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2023.136078

•Pseudotetrahedral C2-symmetrical Co/Zn(II)-achiral Schiff base complexes.•X-ray molecular structure and N2O2-coordination sphere around the metal atom.•Coordination of two unsymmetrical N,O-chelates induces Λ/Δ-chirality at-metal as a racemic mixture.•Thermal and electrochemical analyses.•Combined analyses of experimental and theoretical (DFT/TD-DFT) results. Reaction of achiral Schiff base ligands 1-((X-phenylimino)methyl)naphthalen-2-ol {X = 2-ethyl (HL1) or 4-methyl (HL2)} with cobalt(II) or zinc(II) acetate provided the corresponding bis[1-((X-phenylimino)methyl)naphthalen-2-olato-k2N,O]cobalt(II) or zinc(II) {X = 2-ethyl: M = Co (1) and Zn (2) or X = 4-methyl: M = Co (3) and Zn (4)} complexes. The molecules crystallize in the centrosymmetric space groups R–3 (1) and P–1 (3 or 4). Molecular structures determinations showed coordination of two molecules of the N,O-chelate ligands to the metal ion and formation of pseudotetrahedral complexes with C2-symmetry. Furthermore, coordination of two unsymmetrical achiral N,O-chelates induces Λ/Δ-chirality at the metal atom as a racemic mixture in the centrosymmetric space groups. Structural analyses further reveal that incorporation of 2-ethyl (1) or 4-methyl (3 or 4) group on the N-bound phenyl ring leads to an increase of both the O1-M-O2 and N1-M-N2 bond angles on going from 1 to 3 or 4, with the N1-M-N2 angle increasing to a much greater extent. The fair matching of the experimental and simulated powder X-ray diffraction patterns confirms the phase purity of bulk microcrystalline sample. Differential scanning calorimetry (DSC) results suggest an irreversible phase transformation from solid crystals to isotropic-liquids and subsequent thermal stability of the complexes. Cyclic voltammograms indicate a quasi-reversible two one electron charge transfer processes for 1 or 3 in N,N-dimethylformamide (DMF). Optimized geometry and excited state properties by density functional theory (DFT) and time dependent-density functional theory (TD-DFT) calculations correspond well to the experimental results. Pseudotetrahedral C2-symmetrical bis[1-((X-phenylimino)methyl)naphthalen-2-olato-k2N,O]cobalt(II) and zinc(II) {X = 2-ethyl: M = Co (1) and Zn (2); X = 4-methyl: M = Co (3) and Zn (4)} with Λ/Δ-chirality induction at-metal, a racemic mixture of two stereoisomers in the centrosymmetric space groups. [Display omitted]