From Mesocates to Helicates: Structural, Magnetic and Chiro‐Optical Studies on Nickel(II) Supramolecular Assemblies Derived from Tetradentate Schiff Bases

Abstract

The systematic reactions of a family of tetradentate pyridyl/imine and quinolyl/imine racemic or enantiopure Schiff bases with Ni(NO ) or Ni(ClO ) in the presence of sodium azide yielded, as a function of the starting racemic, chiral or achiral base, a set of chiral, meso or achiral complexes. In all cases, the compounds consist of two Ni cations linked by a double azido bridge in its end-on coordination mode. All the dimers exhibit a mesocate supramolecular structure and one of them, the unprecedented mix of helicate and mesocate in 2:1 ratio. The transition from mesocate to helicate conformation has been reached by tuning the flexibility of the central spacers of the Schiff bases and the size of the substituents. Electronic circular dichroism (ECD) studies have been performed for two pairs of enantiomers and interpreted by means of DFT calculations. Susceptibility measurements show a ferromagnetic coupling between the Ni cations mediated by the end-on azido bridges.

Steric and Electronic Factors Affecting the Conformation of Bimetallic CuI Complexes: Effect of the Aliphatic Spacer of Tetracoordinating Schiff‐Base Ligands

“…[10][11][12][13][14][15][16] The preferential formationo fahelicate or its conformer mesocate, can be guided by subtle differences in the design of the ligands, while other factorsa re currently investigated because of the interesti ns upramolecular chemistry by including new rules of design. [17] In bimetallic complexes, where the coordinating fragmentso ft he ligands are tethered by alkyl bridges,t he numbero fm ethylene units in the bridge can modulate the formation of one of the conformers, mesocate or helicate. This has been named the odd-even rule by the Albrecht's work on bis-catecholate bimetallic complexes.…”

Ni(II) Dimers of NNO Donor Tridentate Reduced Schiff Base Ligands as Alkali Metal Ion Capturing Agents: Syntheses, Crystal Structures and Magnetic Properties

“…2 /Σ(χMT)exp 2 . The best-fitting parameters are found to be J = 3.97(8) cm -1 , g = 2.08(2), and θ = −1.16 K with R = 1.2 × 10 -5 (for complex 1); J = 4.66(2) cm -1 , g = 2.14 (9), and θ = −1.49 K with R = 1.52 × 10 -5 (for complex 2); and J = 5.50(1) cm -1 , g = 2.30(2), and θ = −1.29 K with R = 2.3 × 10 -6 (for complex 3) (Table 2). Here, it is worth mentioning that consideration of only the anisotropy term (D) in the spin Hamiltonian yielded poor data fitting at low temperature.…”

“…During the past few decades, synthesis and characterizations of polynuclear transition metal complexes and their magnetic and electronic properties have received much attention from chemists due to their potential applications in magnetic ordering and catalytic and biological mimicking [1][2][3][4][5][6][7][8][9]. A common strategy for the synthesis of such polynuclear complexes is to bind the metal centers by a single atom bridge.…”

Synthesis, crystal structures, antiproliferative activities and reverse docking studies of eight novel Schiff bases derived from benzil

“…Schiff bases are important compounds in chemistry and biochemistry due to their flexibility (Mayans et al, 2018;Pramanik et al, 2018), easy preparation (Erxleben, 2018;ISSN 2053ISSN -2296 # 2020 International Union of Crystallography Ganguly et al, 2014), exceptional chelating ability (Malik et al, 2018;Vardhan et al, 2015) and to their broad spectrum of biological and pharmaceutical activities, such as antimicrobial (Anush et al, 2018;Unver & Bektas, 2018;Bharathi et al, 2018;Carreñ o et al, 2018), anti-inflammatory (Venkatesan et al, 2018;Farag et al, 2017;Bano et al, 2017;Khayyat et al, 2015) and anticancer properties (Unver & Bektas, 2018;Santhosh Kumar et al, 2018;Kalaiarasi et al, 2018;Ariyaeifar et al, 2018). Thus, the chemistry of Schiff bases has always been a promising field of research.…”