ABSTRACT
The sandwich-type tungstogermanates [Cu(3)(H(2)O)(B-beta-GeW(9)O(33)(OH))(B-beta-GeW(8)O(30)(OH))](12-) (1), [Co(H(2)O)(2){Co(3)(B-beta-GeW(9)O(33)(OH))(B-beta-GeW(8)O(30)(OH))}(2)](22-) (2), and [Mn(H(2)O)(2){Mn(3)(H(2)O)(B-beta-GeW(9)O(33)(OH))(B-beta-GeW(8)O(30)(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-beta-GeW(8)O(31)) and (B-beta-GeW(9)O(34)), 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 C(s) 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 Co(2+) or Mn(2+) 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 Cu(2+) ions in 1 and between the three Mn(2+) ions in 3. On the other hand, polyanion 2 possesses ferromagnetic interaction of the Co(2+) ions. The best least-squares fit values for 2 are J(z) = 7.9 cm(-1), J(z) = 3.1 cm(-1), J(y) = 2.4 cm(-1), g(z) = 6.77 cm(-1), and g(xy) = 4.15 (R = 2.6 x 10(-2)).
