Purple molybdenum bronzes

The purple molybdenum bronzes have the general formula AMoeOn, where A = Li, Na, K or Tl. The potassium and thallium members have trigonal structures while the Li and Na compounds show different types of distortions, which result in monoclinic symmetry. The ideal value of A in this structure should be 1.0 however, it seems to be closer to 0.9 for all members except Tl. Only for the Na compound has a slight stoichiometry range (0.84 < x < 0.96) been observed. The origin of this behavior is not clear although it may be electronic in nature. 

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