Study On Synthesis And Properties Of Chiral Evans-Showell Type Polyoxometalate Compounds

Chiral polyoxometalates, which may combine the advantage of polyoxometalates with the importance of chirality, have attracted particular attention in recent years. The design and synthesis new materials based on chiral POMs, is a topical and challenging area owing to their potential applications in catalysis, nonlinear optics, medicine.In this paper, starting with the point of molecular design, we successfully obtained a series of new chiral POMs and racemic ones based on Evans-Showell type polyoxoanions [Co2Mo10O38H4]6-. These compounds have been characterized by element, IR, UV-Vis, PXRD, TG, CD spectra, single-crystal X-ray analysis. And the catalytic properties and nonlinear optics properties have been investigated.1. Four compounds have been synthesized by Evans-Showell type polyoxoanions [Co2Mo10O38H4]6- and lanthanide cations (Ln= Sm3+, Eu3+). And the reaction temperature playing a crucial role to mediate the formation of racemic species vs.conglomerates in the field of POMs, is for the first time demonstrated. Compounds 1 and 2 are chiral species, obtained at the lower temperature, showing a mono-supporting structure. When the reaction temperature was increased, racemic compounds 3 and 4 were got. They show a 1D ladderlike structure constructed from left-handed chain and right-handed chain linked by lanthanide cations, which represent the first 1D self assembly based on Evans-Showell type polyoxometalate. All of the four compounds acted as Lewis acid catalysts through a heterogeneous manner to prompt cyanosilylation with excellent efficiency. (NH4)3[Ln(H2O)6][Co2Mo10H4O38]-6H20 [Ln= Sm(1), Eu(2)] [Ln(H2O)5][Ln(H2O)7][Co2Mo10H4038]-6H20 [Ln= Sm(3), Eu(4)]2. Five chiral compounds (5-9) and a racemic one (10) have been synthesized by Evans-Showell type [CO2MO10O38H4]6- polyoxoanion, transition metal cations and 3-(4-pyridyl)acrylic(4-Hpya). Isostructural compounds 5-9 as a conglomerate of two enantiomerically pure crystals in the absence of any chiral source. Their structures comprise one chiral [CO2Mo10H4O38]6- anion, one [M(H2O)6]2+ unit and four protonated 4-H2pya ligands. The chiral [CO2Mo10H4O38]6- polyoxoanions can be connected up together by extensive hydrogen-bonding interactions among terminal oxygen atoms, coordinated water molecules, and organic ligands to construct a 3D supramolecular chiral framework. To our best knowledge, compounds 5-9 represent the first examples of chiral hybrid species based on Evans-Showell type polyoxometalates. The second harmonic generation activities of them were measured, which shows that the chiral species have potential in the application for NLO material.ompound 10 is built up of six protonated 4-H2pya and isolated[Co2Mo10H4O38] polyoxoanions, without any metal cation. [4-H2pya]4[M(H2O)6][Co2Mo10H4O38]·5H20 [M= Co(5), Ni(6), Cu(7), Zn(8), Cd(9)] [4-H2pya]6[Co2Mo10H4O38]·10H2O (10)...