Crystal structures of [NEt(3)H](5)[XCo(II)W(11)O(39)]center dot 3H(2)O (X=P or As)

The orthorhombic crystal structures of [NEt(3)H](5)[XCo(II)W(11)O(39)]. 3H(2)O for X=P and As have been determined with data collected at room temperature, and for X=P at -degrees 100C, using Mo-K alpha radiation. For the latter the space group is Pna2(1), a=21.670(11), b=14.805(4), c=20.393(5) Angstrom and Z=4. The structure consists of chains of alpha-Keggin-type molecules joined by W-O-Co links aligned in the a-axis direction. The Co/W occupancy at the link is disordered, with 61% Co on one side and 39% on the other. Further probable disorder, by lamellar merohedral twinning on (001) and by misorientation of the triethylammonium ions, has obscured the ethyl groups and the water molecules. In polarized light the crystals are-deep wine-red normal to the chains (in the b direction), but-nearly colourless in the a and c directions. The structure of the arsenate is similar to that of the phosphate.