Chiral Ligand-Driven Systematic Synthesis of Coordination Polymers with Non-centrosymmetric Structures

Chirality is an important concept in chemistry revealing intriguing optical properties such as circular dichroism (CD), circularly polarized luminescence (CPL), etc. As one of the non-centrosymmetric (NCS) classes, chiral materials with extended structures may exhibit unique nonlinear optical (NLO) properties, such as second-harmonic generation (SHG). In this Concept article, a series of recently discovered NCS coordination polymers (CPs) from use of carefully designed chiral organic ligands are reviewed. Combining several metal cations such as lanthanides, lead, zinc, and cadmium with rigid chiral ligands has resulted in interesting CPs with both polar and nonpolar structures. Detailed structures, SHG properties, and structure-property relationships are provided. The importance of hyperpolarizability formed by intermolecular hydrogen boding interactions to SHG is emphasized.

Nickel(II) complexes based on L-amino-acid-derived ligands: synthesis, characterization and study of the role of the supramolecular structure in carbon dioxide capture

The formation of the symmetrical μ3-carbonate-bridged self-assembled trinuclear NiII complex Na2{[Ni(LO)2(H2O)]3(μ3-CO3)} (LO is the carboxylate anion of a L-tyrosine derivative), involves atmospheric CO2 uptake. The asymmetric unit of the complex comprises an octahedral coordination for the NiII with two L-tyrosine-based ligands, a water molecule and one O atom of the carbonate bridge. The Ni3-μ3-CO3 core in this compound is the first reported of this kind according to the Cambridge Structural Database (CSD). The supramolecular structure is mainly sustained by hydrogen bonds developed by the phenolic functionality of the L-tyrosine moiety of one ligand and the carboxylate group of a neighbouring ligand. The crystal packing is then characterized by three interpenetrated supramolecular helices associated with a diastereoisomer of the type R-supP, which is essential for the assembly process. Magnetic susceptibility and magnetization data support weak ferromagnetic exchange interactions within the novel Ni3-μ3-CO3 core. The NiII complex obtained under the same synthetic conditions but using the analogous ligand derived from the amino acid L-phenylalanine instead of L-tyrosine gives rise to to a mononuclear octahedral system. The results obtained for the different complexes demonstrate the role of the supramolecular structure regarding the CO2 uptake property for these NiII-amino-acid-based systems.

Exploration of disaccharide as reference towards chiral recognition by the kinetic method

RATIONALE

A potential use of disaccharides was found as reference compounds in the kinetic method for chiral recognition and enantiomeric quantification.

METHODS

The experimental procedure consists of three steps: (1) mixing a metal salt, an analyte and a disaccharide at a molar ratio of 1:2:2 with an analyte concentration of 20 μM; (2) introducing the mixture into an electrospray ionization (ESI) mass spectrometry source; (3) isolating the ion [M^II (ref*)₂ (A) - H]⁺ and subjecting it to dissociation. Then through the relative ratio of two product ions combined with the kinetic method, chiral recognition and enantiomeric quantification can be achieved.

RESULTS

The method was verified with good chiral recognition for ten chiral amino acids and three chiral drugs. Among the ten amino acids, Tyr was observed to show best chiral selectivity (R_chiral  = 1.62) and good linearity with the correlation coefficient R²  = 0.9991 for the quantitation of the enantiomeric excess (ee) of D-Tyr. Among the tested chiral drugs, naproxen showed best chiral selectivity with R_chiral  = 1.56 and good linearity with the correlation coefficient R²  = 0.9997 for the quantitation of the ee of R-naproxen.

CONCLUSIONS

This established approach proves that a disaccharide can serve as a reference compound for chiral recognition using the kinetic method.

Design and application of a fluorogenic receptor for selective sensing of cations, small neutral molecules, and anions

An unprecedented single multi-analyte fluorogenic receptor, a sodium salt of N-(methyl-2-thiophenyl)-tyrosine (NaHTyrthio), is reported for the selective sensing of cations (Cu²⁺), small neutral molecules (nitrobenzene and aniline) and anions (F⁻) by variable spectral responses.

Integration of a semi-rigid proline ligand and 4,4'-bipyridine in the synthesis of homochiral metal-organic frameworks with helices

A pair of 3-D homochiral metal-organic frameworks (HMOFs) based on a mixed semi-rigid 5-(2-carboxypyrrolidine-1-carbonyl)isophthalate (PIA) ligand and rigid 4,4'-bipyridine (bipy), [Co3((R)-PIA)2(bipy)3]·6H2O (1-D) and [Co3((S)-PIA)2(bipy)3]·6H2O (1-L) are synthesized and structurally characterized. They are enantiomers and exhibit three-dimensional open frameworks. In each structure, the PIA ligands link the Co centers into homochiral frameworks with large open channels that are occupied by the bipy ligands. Interesting helical chains built from the connectivity between PIA ligands and Co centers are presented. Antiferromagnetic coupling is observed in 1-D. These results demonstrated that the mixed ligand approach is successful for the construction of HMOFs.