A new compound Na3H3[Co(en)3]2[Co4(H2O)2(PW9O34)2]·11H2O 1 (en = ethylene-diamine) has been synthesized under hydrothermal conditions and characterized by IR, TGA, and single-crystal X-ray diffraction analysis. Crystal data: monoclinic, space group C2/c, a = 26.336(5), b = 18.135(2), c = 22.751(4) , β = 123.039(7)° and Z = 4. X-ray crystallographic study on compound 1 reveals that it includes a Weakley-type sandwich polyoxoanion [Co4(H2O)2(PW9O34)2]10-, two complex ions [Co(en)3]2+, three Na+ ions (one Na(1) and two Na(2)), and eleven crystallographic water molecules. The sandwich polyoxoanions are linked by Na2 to form 2D layers parallel to the (100) plane, and these layers are further connected by Na1 along the a-axis to generate a 3D structure.
