[en] Two new tellurites, NH₄RbTe₄O₉.2H₂O and NH₄CsTe₄O₉.2H₂O have been synthesized and characterized. The compounds were synthesized hydrothermally, in near quantitative yields, using the alkali metal halide, TeO₂, and NH₄OH as reagents. The iso-structural materials exhibit layered, two-dimensional structural topologies consisting of TeO_x (x=3, 4, or 5) polyhedra separated by NH₄⁺, H₂O, Rb⁺ or Cs⁺ cations. Unique to these materials is the presence of TeO₃, TeO₄, and TeO₅ polyhedra. Thermogravimetric and infrared spectroscopic data are also presented. Crystal data: NH₄RbTe₄O₉.2H₂O: Monoclinic I2/a (no. 15), a=18.917(3) A, b=6.7002(11) A, c=21.106(5) A, β=101.813(2)^o, V=2618.5(9) A³, Z=8; NH₄CsTe₄O₉.2H₂O: Monoclinic I2/a (no. 15), a=18.9880(12) A, b=6.7633(4) A, c=21.476(2) A, β=102.3460(10)^o, V=2694.2(3) A³, Z=8. - Graphical abstract: Two unprecedented tellurites, NH₄ATe₄O₉.2H₂O (A=Rb or Cs) have been synthesized and characterized. The materials represent rare examples of tellurites that contain TeO₃, TeO₄, and TeO₅ polyhedra in the same compound. All of the polyhedra are in asymmetric polar coordination environments attributable to their stereo-active lone-pair