High-nuclearity Ni-substituted polyoxometalates: a series of poly(polyoxotungstate)s containing 20–22 nickel centers.

Three high-nuclearity Ni-substituted polyoxotungstates (POTs)--[Ni(enMe)2(H2O)2]2[Ni(H2O)6]2[Ni(enMe)2][Ni(H2O)2]1.5[HNi20X4W34(OH)4O136(H2O)6(enMe)8]·11 H2O (3), [Ni(en)2(H2O)]2[H8Ni21X4W34(OH)4O136(en)10(H2O)5]·22 H2O (4), and [Ni(enMe)2]2[H6Ni22X4W34(OH)4O136(H2O)6(enMe)10]·18 H2O (5), in which en = ethylenediamine, enMe = 1,2-diaminopropane, X = 0.5 P+0.5 Ge--were made under hydrothermal conditions and characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, powder X-ray diffraction, and single-crystal X-ray diffraction. The structures of 3–5 can be viewed as novel derivatives of [H6Ni20P4W34(OH)4O136(enMe)8(H2O)6]·12 H 2O (1) and [Ni(en)2(H2O)]2[H8Ni20P4W34(OH)4O136(en)9(H2O)4]·16 H 2O (2), which both contain 20 nickel ions per structural unit. Compound 3 is the first example of a 1D cluster chain constructed from Ni20-substituted polyanions [HNi20X4 W34(OH)4O136(H2O)6(enMe)8]11− and [Ni(enMe)2]2+ bridges. Compound 4 is a novel cluster–organic chain built by Ni21-substituted polyanions [H8Ni21X4W34(OH)4O136(en)10(H2O)5]4− and en molecule bridges. Compound 5 is a discrete POT with 22 Ni centers, and is not only the largest nickel-substituted POT, but also contains the highest number of nickel ions in one polyanion to date. Magnetic measurements illustrate that overall ferromagnetic interactions exist in 1–5. The magnetic behavior of 1 and 2 was theoretically simulated by the MAGPACK magnetic program package.