Assemblies And Catalysis Properties Of Coordination Polymers On The Basis Of Amino Acid Derivatives

Metal complexes of amino acid derived reduced Schiff base ligandshas been a hot topic due to the formation of fascinating chiral structuresand potential performances, for example, molecular recognition,molecular catalysis, and ion exchange, separation. In this paper, sixN-(pyridylmethyl)-amino acid ligands have been synthesized andcharacterized by IR spectra and1H NMR. Then a series of newcoordination polymers involving the synthesized amino acid as bridgingligands and various transition metal ions as nodes have been obtained.Their structures and catalytic properties were further investigated. Thecontents of this paper were described as follows:1. Firstly, a pair of enantiomeric ligands,N-(2-pyridylmethyl)-L-valine (2L-Hvgly) and N-(2-pyridylmethyl)-D-valine (2D-Hvgly) were synthesized by reacting amino acid with2-pyridinecarboxaldehyde. The TG and fluorescence of the ligands weredetermined. The structures of the ligands were investigated by1H NMR,IR. Secondly, reaction of2L(D)-Hvgly with different transition metals,afforded four new chiral coordination polymers Zn2(2L-vgly)2Cl2(H2O)(1),{[Cd(2L-vgly)(DMF)(H2O)]·ClO4}n(2),[Cd2(2L-vgly)2Cl3]n(3),[Cd2(2D-vgly)2Cl3]n(4). X-ray single-crystal diffraction analysis revealsthat compound1is a binuclear structure, which forms3D supramolecularframework via hydrogen bondings, while2features a one-dimensionalstructure. Complexes3and4are two enantiomers, which showone-dimensional double helix chains. Thirdly, the spectroscopic, thermal,and luminescent properties of1–4have also been investigated.2. N-(3-pyridylmethyl)-L-valine (3L-Hvgly) andN-(3-pyridylmethyl)-D-valine (3D-Hvgly) were synthesized by reactingvaline with3-pyridinecarboxaldehyde. Then3L(D)-Hvgly were chossento assemble with different metal ions, and three coordination polymers{[Cu(3L-vgly)(Ac)(H2O)]·2H2O}n(5),{[Cu(3D-vgly)(Ac)(H2O)]·2H2O}n(6),[Zn(3L-vgly)Cl2]n(7), wereobtained. X-ray single-crystal diffraction analysis reveals that compounds 5and6are enantiomers and display similar1-D coordination frameworks(5for D-chained structure,6for L-chain structure), which present3Dsupramolecular frameworks via hydrogen bondings. And7shows a2Dsupramolecular layer. In addition, the luminescent properties in the solidstate of the free organic ligand3L(D)-Hvgly and complexes5–7wereinvestigated.3. Two chiral amino derivatives4L-Hvgly and4D-Hvgly have beensynthesized and characterized by H-NMR. Then using these two ligandsas starting material, nine coordination compounds{[Cu(4L-vgly)Cl2]2·0.5H2O}n(8),{[Cu(4L-vgly)Cl]2·NO3·H2O}n(9),{[Pb(4L-vgly)Cl]·NO3}n(10),{[Co(4L-vgly)·3H2O]·Ac}n(11),{[Co(4D-vgly)·3H2O]·Ac}n(12)、{[Zn2(4L-vgly)2H2O]·(NO3)2·H2O}n(13),{[Zn2(4D-vgly)2H2O]·(NO3)2·H2O}n(14),{[Zn(4L-vgly)Cl]·2H2O}n(15)and {[Zn(4D-vgly)Cl]·2H2O}n(16) havebeen synthesized and characterized by X-ray diffraction analysis. Theresults reveal that compounds8–12are one-dimensional structures, whilecompounds13–16are two pairs of enantiomers and displaythree-dimensional chiral structures. Finally, the spectroscopic, thermal,and luminescent properties of8–16have also been investigated.4. Catalytic property of coordination compound1-16was studied.The results reveal that compound5is a good catalyst for enantioselectiveoxidation of prochiral sulfides. The optimal condition: substrate (1mmol)and catalyst5(0.05mmol) were mixed in EtOH (8ml) at30°C, whichwas warmed at30°C over10min. Under this condition, both theconversion and chemoselectivity are up to99%, but the enantioselectiverate is up to23%. And further investigation of the catalytic mechanism isdue to the metal center acts as an open site to combine with oxidant(H2O2) and to attack the substrate.