title: Chirality at metal and helical ligand folding in optical isomers of chiral bis(naphthaldiminato)nickel(II) complexes.
abstract: Enantiopure bis[{(R or S)-N-1-(Ar)ethyl-2-oxo-1-naphthaldiminato-κ(2)N,O}]nickel(ii) complexes {Ar = C6H5 ( or ), p-OMeC6H4 ( or ), and p-BrC6H4 ( or )} are synthesized from the reactions between (R or S)-N-1-(Ar)ethyl-2-oxo-1-naphthaldimine and nickel(ii) acetate. Circular-dichroism spectra and their density-functional theoretical simulation reveal the expected mirror image relationship between the enantiomeric pairs / and / in solution. CD spectra are dominated by the metal-centered Λ- or Δ-chirality of non-planar four-coordinated nickel, this latter being in turn dictated by the ligand chirality. Single crystal structure determination for and shows that there are two symmetry-independent molecules (A and B) in each asymmetric unit that give a Z' = 2 structure. Two asymmetric and chiral bidentate N^O-chelate Schiff base ligands coordinate to the nickel atom in a distorted square planar N2O2-coordination sphere. The conformational difference between the symmetry-independent molecules arises from the "up-or-down" folding of the naphthaldiminato ligand with respect to the coordination plane, which creates right- (P) or left-handed (M) helical conformations. Overall, the combination of ligand chirality, chirality at the metal and ligand folding gives rise to discrete metal helicates of preferred helicity in a selective way. Cyclic voltammograms (CV) show an oxidation wave at ca. 1.30 V for the [Ni(L)2]/[Ni(L)2](+) couple, and a reduction wave at ca. -0.35 V for the [Ni(L)2]/[Ni(L)2](-) couple in acetonitrile.
authors.affiliation: Department of Chemistry, Jahangirnagar University, Dhaka-1342, Bangladesh. enamullah@juniv.edu.
authors.forename: Mohammed
authors.initials: M
authors.lastname: Enamullah
authors.affiliation: Department of Chemistry, Jahangirnagar University, Dhaka-1342, Bangladesh. enamullah@juniv.edu.
authors.forename: Mohammad Abdul
authors.initials: MA
authors.lastname: Quddus
authors.affiliation: Department of Chemistry, Jahangirnagar University, Dhaka-1342, Bangladesh. enamullah@juniv.edu.
authors.forename: Mohammad Rezabul
authors.initials: MR
authors.lastname: Hasan
authors.affiliation: Department of Chemistry, University of Pisa, Via Moruzzi 13, 56124 Pisa, Italy. gennaro.pescitelli@unipi.it.
authors.forename: Gennaro
authors.initials: G
authors.lastname: Pescitelli
authors.affiliation: Department of Chemistry, University of Pisa, Via Moruzzi 13, 56124 Pisa, Italy. gennaro.pescitelli@unipi.it.
authors.forename: Roberto
authors.initials: R
authors.lastname: Berardozzi
authors.affiliation: Institut für Anorganische Chemie und Strukturchemie, Universität Düsseldorf, Universitätsstr. 1, D-40225 Düsseldorf, Germany. janiak@uni-duesseldorf.de.
authors.forename: Gamall
authors.initials: G
authors.lastname: Makhloufi
authors.affiliation: Institut für Anorganische Chemie und Strukturchemie, Universität Düsseldorf, Universitätsstr. 1, D-40225 Düsseldorf, Germany. janiak@uni-duesseldorf.de.
authors.forename: Vera
authors.initials: V
authors.lastname: Vasylyeva
authors.affiliation: Institut für Anorganische Chemie und Strukturchemie, Universität Düsseldorf, Universitätsstr. 1, D-40225 Düsseldorf, Germany. janiak@uni-duesseldorf.de.
authors.forename: Christoph
authors.initials: C
authors.lastname: Janiak