Comprehensive studies by HREM, SAED, and EDXS have been recently devoted to the real structure of the ternary reduced molybdenum oxides in the series Mn±δMo4n+2O6n+4 with M = Sn,In. These compounds contain condensed clusters Mo4n+2O8n+10 with a core of n transedge-sharing molybdenum octahedra. The individual clusters are interconnected via common oxygen atoms. of course, the appropriate choice of counter-cations M is essential for the stability of the clusters, whose core of condensed molybdenum octahedra is a more or less extended metal-metal bonded structure. In tin oxomolybdates condensed clusters with n = 2,3 have been observed, in indium oxomolybdates with n = 3,4,5,6. In Sn2Mo10O16 and Sn2.8Mo14O22 each Sn atom provides 2 electrons to the cluster, in In5Mo18O28, e.g., with n = 4 an In57+ polycation, a metal-metal bonded unit itself, provides 7 electrons.

It became obvitalicous that both tin and indium oxomolybdates undergo a structure transformatitalicon when irradiated a 300kV electron mitaliccroscope (Philips CM30/ST, Cs = 1.15mm).