Monoclinic single crystals of Cd(H2O)(2)[C6H3(COO)(2)(-COOH)] have been prepared in aqueous solution at 80 ° C. Space group C2/c (no. 15), a = 1973.0(2), b = 910.74(7), c 1336.81(10) pm, P = 117.897(8)°, V = 2.1230(3) nm(3), Z = 8. Cd2+ is coordinated in a moderately distorted pentagonal bipyramidal fashion by five oxygen atoms stemming from the monohydrogentrimesinate anions in the equatorial plane and two water molecules in the apical positions (Cd-O 224.0(2) - 255.0(2) pm). The connection of Cd2+ with [C6H3(COO)(2)(COOH)](2-) yields a two-dimensional coordination polymer. The atoms of the monohydrogentrimesinate anion form in good approximation a common plane. Thermogravimetric analysis in air shows that the dehydrated compound is stable up to 390 ° C. Further decomposition yields CdO.