A novel, two-dimensional tellurite of molybdenum(VI), (NH4) 6Mo8Te8O43•H2O, has been isolated as single crystals in a hydrothermal reaction and characterized by single-crystal X-ray diffraction, infrared spectroscopy, and thermal analysis. Pertinent crystal data are as follows: trigonal space group P3h, a = 12.124(4) Å, c = 8.130(3) Å, Z = 1. Its strucrure consists of (Mo 8Te8O43)6- layers interleaved with ammonium ions. The novel feature of the anionic layer is that it contains two anions, discrete [Mo2O7]2- anions residing in an extended framework of (Mo6Te8O36) 4- anions made by corner connection of edge-shared bi-octahedral Mo2O10 units, TeO3 pyramids, and TeO 4 units with SF4 geometry. Its decomposition temperature is 371 °C. © 1999 American Chemical Society.