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Solid-state to solution helicity inversion of pseudotetrahedral chiral copper(ii) complexes with 2,4-dihalo-salicylaldiminate ligands


Kordestani, Nazanin; Amiri Rudbari, Hadi; Bruno, Giuseppe; Rosario, Scopelliti; Braun, Jason D; Herbert, David E; Blacque, Olivier; Correia, Isabel; Zaman, Mohammad Al-moktadir; Bindu, Mortuza Mamun; Janiak, Christoph; Enamullah, Mohammed (2020). Solid-state to solution helicity inversion of pseudotetrahedral chiral copper(ii) complexes with 2,4-dihalo-salicylaldiminate ligands. Dalton Transactions, 49(24):8247-8264.

Abstract

The enantiopure Schiff bases (R or S)-N-1-( phenyl)ethyl-2,4-X-1,X2(-)salicylaldimine (X-1, X-2 = Cl, Br, I) coordinate to copper(II) and provide pseudotetrahedral bis[(S or R)-N-1-(phenyl)ethyl-(2,4-X-1,X-2-salicylaldiminato.2N,O)]-./.-Cu(II) (kappa N-2,O]-Delta/Lambda-Cu(II)(Delta/Lambda-Cu-R o Delta/Lambda-Cu-S). An induced Lambda and Delta-chirality at-metal centre has been launched along the C-2-axis of the molecule. Steric constraints brought by halogen substituents on the coordinating salicylal ring provide diastereoselectively Lambda-Cu-R or Delta-Cu-S as major and Delta Cu-R or Delta-Cu-S as minor diastereomers at solid-state, as evidenced by X-ray crystal structures and PXRD analyses. These results reveal inversion of induced chirality at-metal in comparison to the similar complexes without halogen substituents on the salicylal ring. Electronic circular dichroism (ECD) spectra show mirror-image relationships, confirming enantiomeric excess of the R or S-ligated complexes in solution. Comparisons of experimental and simulated ECD spectra suggest diastereomeric excess of Delta-Cu-R or Delta-Cu-S in solution which correspond to an inversion from the found solid-state Delta-Cu-R or Delta-Cu-S as major diastereomers. In addition, the optimized gas-phase structures also reveal Delta-Cu-R or Delta-Cu-S as slightly more stable than Delta-Cu-R or Delta-Cu-S. Thus, solid-state versus solution (or gas-phase) studies also indicate an interconversion of induced chirality (helicity inversion) at-metal from Delta-Cu-R or Delta-Cu-S to Delta-Cu-R or Delta-Cu-S. Thermal stability increases with the molecular weight of the complexes following Cl < ClBr < Br < I substituents. Hirshfeld surface analyses explore the strongest halogen (ortho)-halogen (para) interactions between two molecules in Delta-Cu-R3 or Delta-Cu-S3 at a distance shorter than the sum of the van der Waals radii of the two iodine atoms, provide a brilliant red spot on the dnorm surfaces. EPR spectra along with simulation suggest an axial symmetry with g(z) > g(x,y) > 2.0 and values for g(z)/A(z) >= 135 cm indicate pseudotetrahedral geometry for the complexes.

Abstract

The enantiopure Schiff bases (R or S)-N-1-( phenyl)ethyl-2,4-X-1,X2(-)salicylaldimine (X-1, X-2 = Cl, Br, I) coordinate to copper(II) and provide pseudotetrahedral bis[(S or R)-N-1-(phenyl)ethyl-(2,4-X-1,X-2-salicylaldiminato.2N,O)]-./.-Cu(II) (kappa N-2,O]-Delta/Lambda-Cu(II)(Delta/Lambda-Cu-R o Delta/Lambda-Cu-S). An induced Lambda and Delta-chirality at-metal centre has been launched along the C-2-axis of the molecule. Steric constraints brought by halogen substituents on the coordinating salicylal ring provide diastereoselectively Lambda-Cu-R or Delta-Cu-S as major and Delta Cu-R or Delta-Cu-S as minor diastereomers at solid-state, as evidenced by X-ray crystal structures and PXRD analyses. These results reveal inversion of induced chirality at-metal in comparison to the similar complexes without halogen substituents on the salicylal ring. Electronic circular dichroism (ECD) spectra show mirror-image relationships, confirming enantiomeric excess of the R or S-ligated complexes in solution. Comparisons of experimental and simulated ECD spectra suggest diastereomeric excess of Delta-Cu-R or Delta-Cu-S in solution which correspond to an inversion from the found solid-state Delta-Cu-R or Delta-Cu-S as major diastereomers. In addition, the optimized gas-phase structures also reveal Delta-Cu-R or Delta-Cu-S as slightly more stable than Delta-Cu-R or Delta-Cu-S. Thus, solid-state versus solution (or gas-phase) studies also indicate an interconversion of induced chirality (helicity inversion) at-metal from Delta-Cu-R or Delta-Cu-S to Delta-Cu-R or Delta-Cu-S. Thermal stability increases with the molecular weight of the complexes following Cl < ClBr < Br < I substituents. Hirshfeld surface analyses explore the strongest halogen (ortho)-halogen (para) interactions between two molecules in Delta-Cu-R3 or Delta-Cu-S3 at a distance shorter than the sum of the van der Waals radii of the two iodine atoms, provide a brilliant red spot on the dnorm surfaces. EPR spectra along with simulation suggest an axial symmetry with g(z) > g(x,y) > 2.0 and values for g(z)/A(z) >= 135 cm indicate pseudotetrahedral geometry for the complexes.

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Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Scopus Subject Areas:Physical Sciences > Inorganic Chemistry
Uncontrolled Keywords:Inorganic Chemistry
Language:English
Date:1 January 2020
Deposited On:26 Oct 2020 11:29
Last Modified:27 Oct 2020 21:01
Publisher:Royal Society of Chemistry
ISSN:1477-9226
OA Status:Closed
Publisher DOI:https://doi.org/10.1039/d0dt01649g

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