Copper-, Cobalt-, and Manganese-Containing 17-Tungsto-2-Germanates

The sandwich-type tungstogermanates [Cu3(H2O)(B-β-GeW9O33(OH))(B-β-GeW8O30(OH))]12− (1), [Co(H2O)2{Co3(B-β-GeW9O33(OH))(B-β-GeW8O30(OH))}2]22− (2), and [Mn(H2O)2{Mn3(H2O)(B-β-GeW9O33(OH))(B-β-GeW8O30(OH))}2]22− (3) were synthesized and characterized by single-crystal X-ray diffraction, elemental analysis, thermogravimetric analysis, and infrared spectroscopy. Polyanion 1 is composed of two nonequivalent Keggin units, (B-β-GeW8O31) and (B-β-GeW9O34), linked to each other via three copper(II) ions in such a way that there is a plane of symmetry passing through both Ge atoms and the unique Cu atom, resulting in a sandwich-type structure with Cs symmetry. On the other hand, the monomeric building blocks of 2 and 3 contain the same Keggin fragments as 1, but linked through three octahedrally coordinated Co2+ or Mn2+ ions. The major difference between complex 1 and complexes 2 and 3 is that the latter all lack a plane of symmetry due to a different orientation of the rotated triad. Magnetic measurements indicated antiferromagnetic exchange interactions between the three Cu2+ ions in 1 and between the three Mn2+ ions in 3. On the other hand, polyanion 2 possesses ferromagnetic interaction of the Co2+ ions. The best least-squares fit values for 2 are Jz = 7.9 cm−1, Jz = 3.1 cm−1, Jy = 2.4 cm−1, gz = 6.77 cm−1, and gxy = 4.15 (R = 2.6 × 10−2).