Addition of {M2S2O2}2+, M = Mo, W, to A-α-[PW9O34]9-. Synthesis and Structural Characterizations in the Solid State and in Solution

The [P 2 W 18 M 6 S 6 O 74 (H 2 O) 6 ] 12 - anions, M = Mo, W, were obtained through the stereospecific addition of the dithiocation [M 2 O 2 S 2 ] 2+ to the trivacant A-α-[PW 9 O 34 ] 9 - . K 12 [P 2 W 18 Mo 6 S 6 O 74 (H 2 O) 6 ]·26H 2 O has been isolated as crystals and has been characterized by X-ray diffraction (orthorhombic Pmn 2 1 with a = 31.530(6) Å, b = 19.703(4) Å, c = 18.761(4) Å, Z = 4). The structure of the anion consists of a sandwich-like arrangement of two α-[PW 9 O 34 ] 9 - subunits bridged by three [Mo 2 O 2 S 2 (H 2 O) 2 ] cores. The X-ray diffraction structural analysis showed that one [Mo 2 O 2 S 2 ] bridging unit was rotated through an angle of 180° with respect to the other two. Among the six water molecules attached to the Mo centers, four are directed toward the inner cavity while the two remaining ones are directed out of the cavity. According to the X-ray data, 183 W NMR characterizations of both compounds show the lowering of the local symmetry of the α-[PW 9 O 34 ] 9 - subunit from C 3 v to C s . For [P 2 W 24 S 6 O 74 (H 2 O) 6 ] 12 -, two additional deshielded resonances were observed characteristic of the distribution of the three [W 2 O 2 S 2 (H 2 O) 2 ] bridging units. Infrared data are also given.