Photochemically controlled self-assembly to nano-ring structural polyoxometalate superclusters

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Photochemically controlled self-assembly to giant-ring structural polyoxometalate superclusters is promising for the molecular design of nano-rings in the nanostructure landscape, and has opened up a basis of nanotechnology via a bottom-up approach, starting from polyoxometalate subunits which incorporate functionalities that are appropriate for electronic/magnetic devices. A variety of novel structures and fundamentally significant properties for the polyoxometalate nano-rings have been established: (i)A combination of [AsW_9O_<33>]^<9-> (as building block) and lanthanide (Ln^<3+> as linker) led to the formation of crown-shaped polyoxotungstolanthanoate rings such as [Cs⊂Ln_4(H_2O)_8(AsW_9O_<33>)_4]^<23-> (with windmill structure) and [K⊂Ln_6(H_2O)_<12> (AsW_9O_<33>)_6]^<35-> (with watermill-propeller structure) in the presence of Cs^+ and K^+ in solutions, respectively. Interestingly, the presence of Mg^<2+> induced the formation of [{Eu(H_2O)_2}_2(AsW_9O_<33>)}_4(H_2O)_4(EuW_5O_<18> … More )_2]^<30-> with 3.4-nm length, (ii)Subsequent to our finding of the photoinduced formation of car-tire-shaped Mo-blue nano-rings of {Mo_<142>} and {Mo_<145>} with 3.5 nm diameter, a manipulation of pH level, concentration of Ln^<3+>, and electron donor compounds showed a wide variety of nano-ring clusters such as {Mo_<154>}∞(nano-tube), {Mo_<146>}∞(nano-chain), {Mo_<150>La_2}, {Mo_<120>Ln_6}, {Mo_<130>Ln_<10>}, and {Mo_<150>Ln(MeC_6H_4SO_2)_4} which could be photochemically controlled. The time-resolved ESR spectroscopy was employed for the clarification of initial steps of the reaction, and a pioneering mechanism for the self-assembly to nano-sized Mo-blues has been offered, (iii)It is found that three typed polyoxotungstates sandwiching spin moieties of triangle, trigonal prism, and hexagon are novel single-molecule magnets at low temperatures : for example, K_<11>H[(VO)_3(SbW_9O_<33>)_2]・29H_2O which is a spin-frustrated compound with D_<3h> anion incorporating (VO)_3^<6+>-triangle with V^<IV>…V^<IV> separation of 5.4 Å, is a good model of the magnetization between pure quantum states S=1/2 and 3/2 and provides a new class of single-molecular magnets. "International Symposium on Nano-structures and Physicochemical Properties of Polyoxometalate Superclusters and Related Colloid Particles" was organized by T.Yamase, M.T.Pope, and A.Muller with the support of the present project of JSPS at Shonan village, Kanagawa on Nov.21-25 2004,and a great success of this meeting is reported on Angew.Chem.Int.Ed., 2005, 44, 844-846. Less