Abstract: | The title compounds, potassium pentamolybdenum oxide, KMo5O13, and potassium niobate antimonate or potassium niobium antimony oxide (1/1.76/3.24), KNb1.76Sb3.24O13, were synthesized by solid‐state reactions and are isomorphous in space group Cmcm. The structure of the Mo complex has three unique Mo atoms and consists of MoO6 octahedra sharing edges to form Mo2O6 pairs and Mo3O9 triplets, which, in turn, form layers by sharing corners. These layers are linked together in the 100] direction, yielding a three‐dimensional network similar to that of KSb5O13. This framework delimits interconnected tunnels, running approximately along the 110] and 10] directions, in which K+ ions are located. In the isomorphous KNb1.76Sb3.24O13 structure, one of the Mo sites in KMo5O13 is replaced by Sb and the other two Mo sites have been replaced by Nb/Sb. |