Synthesis, structure and magnetism of a 2-D organic–inorganic hybrid tetra-CoII-substituted sandwich-type Keggin germanotungstate: {[Co(dap)2(H2O)]2[Co(dap)2]2[Co4(Hdap)2(B-α-HGeW9O34)2]}·7H2O

A novel 2-D organic–inorganic hybrid tetra-CoII-substituted sandwich-type Keggin germanotungstate {[Co(dap)2(H2O)]2[Co(dap)2]2[Co4(Hdap)2(B-α-HGeW9O34)2]}·7H2O (1) (dap = 1,2-diaminopropane) has been hydrothermally synthesized and structurally characterized by elemental analyses, IR spectrum, UV spectrum, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and single-crystal X-ray diffraction. Structural analysis shows that 1 displays a rare 2-D (4,4)-topological network constructed by tetra-CoII-substituted sandwich-type Keggin germanotungstate units and [Co(dap)2]2+ bridges. To our knowledge, 1 represents the first 2-D organic–inorganic hybrid cobalt-substituted sandwich-type polyoxotungstate. Magnetic preperties of 1 have been investigated. The decrease of the product of the molar magnetic susceptibility at higher temperatures results from the spin-orbit coupling of the CoII ion and/or the antiferromagnetic interactions whereas the maximum at the lower temperatures is indicative of the ferromagnetic interactions within the tetranuclear CoII spin cluster in the sandwich belt.