Zhi-Ang Zhu

Synthesis and characterization of axial coordination cobalt(III) complexes containing chiral Salen ligands

Abstract Cobalt(III) complexes containing both optically active tetradentate Schiff base ligands, (SB=Salen, MeOSalen, t-Bu-Salen) with axial ligands (L) [Co(SB)L2]ClO4 (L=imidazole (Im), 2-methylimidazole (2-MeIm), 1-methylimidazole (MeIm)) have been prepared and characterized. In addition, the crystal structures of [Co(Salen)(MeIm)2]ClO4 (1c), [Co(MeOSalen)(MeIm)2]ClO4 (2c), and [Co(t-Bu-Salen)(MeIm)2]ClO4 (3c) have been determined by X-ray structure analysis. The properties of these hexacoordinate complexes, such as electronic absorption, circular dichroism spectra, and 1H NMR spectra, have been studied.

Binuclear Transition Metal Complexes of Unsymmetrical Tetradentate Schiff Base Ligands

From the condensation of the Schiff base (HMBP–PHEN) prepared from 5‐methyl‐2‐hydroxybenzophenone (HMBP) and o‐phenylenediamine (PHEN) in the 1:1 mole ratio with substituted salicylaldehydes, a series of homo‐binuclear metal complexes with non‐symmetrical tetradentate Schiff base ligands have been synthesized by the template method. These new types of binuclear metal complexes have been characterized by elemental analyses, IR, UV, FAB and EPR spectroscopy and magnetic properties.

Spectroscopic and theoretical studies on axial coordination of bis(pyrrol-2-ylmethyleneamine)phenyl complexes.

Metal (M = Zn(II), Ni(II), Cu(II)) complexes with tetradentate Schiff base ligand, bis(pyrrol-2-ylmethyleneamine)phenyl, has been synthesized and characterized by elemental analyses, 1H NMR, mass spectra and UV-vis spectra. The standard association constants (Ktheta) and the thermodynamic parameters (Delta(r)Hmtheta,Delta(r)Smtheta,Delta(r)Gmtheta) for axial coordination of imidazole derivatives with these Shiff base complexes were measured with UV-vis spectrophotometric titration. The decrease of enthalpy is found to be the drive of the axial coordination. Our Schiff base complexes can incorporate two axial ligands, except 2-Et-4-MeIm with two big substituents of great steric bulk according to stoichiometry of 1:1. ZnL displays high selectively binding to imidazole due to the steric bulk effect. Supporting density functional theory (DFT) calculations have been undertaken on B3LYP/6-31G(d) level.

Synthesis, spectral and theoretical studies on axial coordination of dinuclear Salen zinc(II) complexes

Two dinuclear chiral Salen Zn(II) complexes Zn2L (L = N,N′-(1R,2R)(−)-1,2-cyclohexylene-bis(3-hydroxybenzylideneimine)) and Zn2L′(OAc)2 (L′ = N,N′-(1R,2R)(−)-1,2-cyclohexylene-bis(3-methoxybenzylideneimine)) with compartmental, potentially hexadentate Schiff-base ligands L and L′ have been synthesized and characterized by elemental analyses, 1H NMR, mass spectra, UV–Vis spectra and circular dichroism spectra. Their axial coordination with N-containing monodentate ligand (imidazole) and bidentate bridging ligands (ethylenediamine and 1,2-propylenediamine) have been studied by circular dichroism spectral titration, UV–Vis spectral titration and molecular modeling. The results of thermodynamic study, including standard association constants (K θ), and thermodynamic parameters ( , , ), together with the energy obtained from molecular modeling suggest that Zn2L can bind two monodentate axial ligands or one bidentate ligand via a bridging mode with its two zinc atoms. However, the complex Zn2L′(OAc)2 can bind two bidentate ligands by a mode that each of its two zinc atoms coordinates to one of the two nitrogen atoms of the bidentate ligand. A small modification on the structure of a complex leads to a distinct binding mode with a certain ligand.

Synthesis of chiral SalenZn(II) and its coordination with imidazole derivatives and amino acid ester derivatives

A chiral complex, SalenZn(II) (S), was synthesized and characterized. Its coordination with imidazole derivatives and amino acid ester derivatives was studied by UV-vis spectrophotometric titrations and CD spectroscopy. The binding constants decreased in the order K (Im)>K (2-MeIm)>K (2-Et-4-MeIm)>K (N-MeIm) for imidazole derivatives, and K (AlaOMe)>K (PheOMe)>K (ValOMe) for amino acid ester derivatives with the same configuration and K D >K L for amino acid esters with different configuration. CD spectra can quantify the strength of SalenZn(II)-ligand interactions, giving results consistent with the magnitudes of the binding constants. Moreover the minimum energy conformations of the adducts were obtained by simulated annealing, and quantum chemical calculations were performed based on those conformations to explain experimental results at the molecular level.