Chiral 1D Metal–Organic Materials Based on Cu(II) and Amino Acid Schiff Bases

Abstract

Four new chiral coordination polymers (CPs), {[Cu(HL n )MeOH]•NO 3 } ∞ (n = 1−4), were obtained using a chiral building block synthesized from the condensation reaction of L-or D-valine with an imidazole aldehyde. These CPs crystallize in a noncentrosymmetric space group P2 1 2 1 2 1 , evidencing that the chirality of the α-amino acid valine is transferred to the structure of the coordination polymer. Moreover, the CPs present a 1D structure with a Cu(II) cation in a square base pyramid geometry formed by two units of chiral ligand and a methanol molecule. The magnetic measurement and theoretical calculations show that the Cu(II) spin carriers are magnetically communicated through the carboxylate bridge, presenting a 1D ferromagnetic chain behavior. Furthermore, four new stable molecular compounds [Cu(HL n )-DMSO] + (n = 1−4), sharing the same chiral building block of CPs, were characterized by circular dichroism (CD). The theoretical electronic excited states of the molecular compounds reproduce the CD experimental spectra showing that the intrinsic chiral activity of the α-amino acid Schiff base is transferred to the Cu(II) centers. Remarkably, using crystal engineering tools, a family of chiral coordination compounds was obtained and analyzed combining several experimental and theoretical approaches, leading to a robust understanding of its chemical and physical properties.

Formation of Ketimines from Aldimines in Schiff Base Condensation of Amino Acids and Imidazole-2-Carboxaldehydes: Tautomerization of Schiff Bases of Amino Acids Resulting in the Loss of Stereogenic Center

“…The structurally reported Schiff base complexes of an imidazole-4-carboxaldehyde with an amino acid give the anticipated aldimine product with copper(II) [36,37], nickel(II), [38], zinc(II) [39], and several lanthanide(III) ions [40,41]. The only example with an imidazole-2-carboxaldehyde gave the unexpected ketimine product [35].…”

3d Magnetic Chains with an Asymmetrical Pyridyl-Triazole Ligand. Influence of Coordination and Local Distortion in the Ligand Field and Magnetometry

“…Coordination polymers (CPs) are extensively studied in diverse fields, such as electrical conduction, gas absorption, magnetism, and luminescence. − Moreover, among all CPs, low-dimensional 1D structures display promising properties in electronics, chiral, absorbent, and catalytical materials …”

“…Coordination polymers (CPs) are extensively studied in diverse fields, such as electrical conduction, gas absorption, magnetism, and luminescence. 1−4 Moreover, among all CPs, low-dimensional 1D structures display promising properties in electronics, 5 chiral, 6 absorbent, 7 and catalytical materials. 8 From the crystal engineering point of view, the rational design of the desired dimensionality and the resulting topology of the 1D material can be achieved by choosing the appropriate metal cations and organic spacers.…”

Chiral Induction in Aluminum Oxo Sulfate Helical Chains

“…Chirality is fascinating and ubiquitous in the universe and life . Chiral inorganic crystalline materials have also been widely studied for their potential applications in asymmetric catalysis/adsorption/separation and second-order nonlinear optics. − One-dimensional helical chains with a DNA-like structure are also among them. , A common synthetic method is a direct method, in which metal ions are directly bound to chiral ligands. − Although this approach seems straightforward, chiral ligands are limited and often not cheap. The other is an indirect method, where the chirality in a small number of chiral inducers is transferred to a large number of crystals without chiral ligands through long-range chemical interactions (such as hydrogen bonds or π–π interactions). − This approach is popular due to its wide applicability.…”

“…2−7 One-dimensional helical chains with a DNA-like structure are also among them. 8,9 A common synthetic method is a direct method, in which metal ions are directly bound to chiral ligands. 10−13 Although this approach seems straightforward, chiral ligands are limited and often not cheap.…”