The acid-base reaction of 1,4-benzodioxane 2-carb-oxy-lic acid with calcium carbonate furnished the centrosymmetric title compound, [Ca(C9H7O4)2(H2O)4], in which the metal ion is octa-hedrally coordinated by two monodentate 1,4-benzodioxane 2-carboxyl-ate liga... ...