Syntheses And Properties Study Of Chiral Metallo Complexes Construced From Terpyridyl-L-α-Leucine Ligand

Design, synthesis, and application of chiral supramolecular functional materials have been attracting chemists’ investigation interest. A novel chiral ligand,(S)-2-((4-([2,2’:6’,2"-terpyridin]-4’-yl)benzyl)amino)-4-methylpentanoic acid (H2tpypa), was intentionally synthetized in this paper. The ligand possesses a hugely conjugated framework and six coordination sites, and through the self-assembly of nickel(Ⅱ) chloride, cobalt(Ⅱ) chloride, cobalt(Ⅱ) nitrate, copper(Ⅱ) chloride, and manganese(Ⅱ) chlorid with this ligand, we got eight new chiral metal-organic coordination complexes, namely,[Ni(Htpypa)2]·4H2O·PF6(1),[Co(Htpypa)2]·4H2O·PF6(2),[Cu2(Htpypa)2]·[Cu(SCN)3]·2H2O (3),[Co2(Htpypa)2(N3)2]·3H2O (4),[Ni2(Htpypa)2(SCN)2]·5H2O (5),[Co2(Htpypa)2(CH3OH)(H2O)]·CH3OH·(PF6)2(6),[Ni2(Htpypa)2(CH3OH)2]·2CH3OH·(PF6)2(7), and [Mn(Htpypa)N(CN)2]n (8), respectively. We have systematically investigated their crystal structures, photoelectronic properties, magnetism and stability.From the X-ray single crystal diffraction analysis, we can see that complexes1and2are isostructural mononuclear complexes, and the six-coordinated metal center is in a slightly distorted octahedron ligated by six nitrogen atoms only from the terpyridine groups of two H2tpypa. The hydrogen bonds between the uncoordinated aminoacid groups bridge those monomers into a one-dimensional double helical chain structure in which two helixes wind aroud each other to form interesting nanosized one-dimensional channels. The overall structural feature of complexes3-7are the chiral dinuclear metallocyclic unit formed by two chiral (Htpypa)" anions in a head-tail bridge style to link with two the same metal ions. Complex3is a complex of Cu(Ⅱ) and Cu(Ⅰ). The central Cu2+ions are five-coordinated with a slightly distorted square-pyramidal coordination symmetry ligated by three nitrogen atoms from the terpyridine of one (Htpypa)-anion, a nitrogen atom and a oxygen atom from the aminoacid group of the other while Cu(Ⅰ) in a triangle geometry coordinates with three terminal ligands SCN-. However, in complexes4-7the central metal ions have a six-coordinated octahedron with oxygen atoms or nitrogen atoms from solvent molecules or counter anions occupied the six coordination site. As for complex8, the central metal ions are also six-coordinated model, but its structure is a one-dimensional polymeric helical chain instead of the dinuclear metallocycles in4-7. Structural analysis shows that the chiral ligand can transmit chirality or further induce new chirality in the resulted chiral metal-organic supramolecular architectures.Complexes1and2were prepared on the condition of pH≈4while the others were gotten on the condition of neutral or nearly neutral condition, and from which we can see that the pH of system is one of the most important factors influencing the structures of complexes. So it can be attained to structure control mainly by pH regulation to adjust the coordination ability of the aminoacid group. However, in the syntheses of complexes3-7, we intentionally adjusted the reaction conditions, such as temperature, reaction solvents, counter anions, etc, but the dinuclear metallocyclic structure units were failed to be broken. So it can be inferred that dinuclear metallocycles are quite stable. The stable constant of complex6is calculated by spectrophotometric titrations method, which further certificates that those chiral dinuclear metallocycles are of high stability.In this paper, the photoelectronic properties of ligand H2tpypa and complexes1-8have been systematically studied and compared (IR, solution-state UV-vis and solid CD spectra). The solid CD spectra illustrate that all complexes have obviously chiral properties. Finally, we also prepared chiral selector of PVC selective electrode based on those chial complexes as carriers. Those PVC film electrodes were prepared by mixing the carrier, plasticizer and PVC in a certain percentage. Those PVC selective electrodes have excellent potential response, and display prior respond to R-mandelic acid and a good recognition for chiral mandelic acid.