Two novel, isostructural, one-dimensional tellurites of molybdenum(VI), (NH4)4Mo6TeO22·2H 2O and Rb4Mo6-TeO22·2H2O, have been synthesized by hydrothermal method. They contain linear (Mo6TeO22)4- anionic chains, parallel to one another and held together by NH4+/Rb+ ions. "Mo6O22" moieties, formed by edge-sharing of six MoO6 octahedra, are connected through tellurium resulting in the (Mo6TeO22)4- anionic chain. Tellurium is four-coordinated with SF4 geometry. The water of crystallization occupies the rest of the lattice. Both compounds have been structurally characterized by single-crystal X-ray diffraction studies. Pertinent crystal data are as follows: for (NH4)4Mo6TeO22·2H 2O, monoclinic space group C2/c, a = 21.354(10) Å, b = 7.761(2) Å, c = 15.508(10) Å, β= 119.34(5)°, Z = 4; for Rb4Mo6TeO22·2H2O, monoclinic space group C2/c, a = 21.410(5) Å, b = 7.757(2) Å, c = 15.507(7) Å, β = 119.68(3)°, Z = 4. Hydrothermal syntheses, structure, powder X-ray diffraction, spectroscopy, and thermal studies of these compounds are described. © 1999 American Chemical Society.