Two-Dimensional Extended (4,4)-Topological Network Constructed from Tetra-Ni<sup>II</sup>-Substituted Sandwich-Type Keggin Polyoxometalate Building Blocks and Ni<sup>II</sup>-Organic Cation Bridges
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Three novel inorganic–organic composite polyoxotungstates {[Ni(dap)2(H2O)]2[Ni(dap)2]2[Ni4(Hdap)2(α-B-HSiW9O34)2]}·7H2O (1), {[Ni(dap)2(H2O)]2[Ni(dap)2]2[Ni4(Hdap)2(α-B-HGeW9O34)2]}·6H2O (2), and {[Ni(dap)2(H2O)]2[Ni(dap)2]2[Ni4(Hdap)2(α-B-PW9O34)2]}·4H2O (3) (dap = 1,2-diaminopropane) have been hydrothermally synthesized and characterized by IR spectra, optical diffuse reflection spectroscopy, elemental analysis, thermogravimetric analysis, and single-crystal X-ray diffraction. Three polyoxotungstates all crystallize in the triclinic space group P1̅, with a = 13.3613(4) Å, b = 13.9821(4) Å, c = 17.0305(5) Å, α = 68.085(10)°, β = 71.179(11)°, γ = 87.876(14)°, Z = 1, R1 = 0.0742, wR2 = 0.1692 for 1, a = 13.338(3) Å, b = 13.978(3) Å, c = 17.049(3) Å, α = 68.159(6)°, β = 71.100(8)°, γ = 87.683(9)°, Z = 1, R1 = 0.0499, wR2 = 0.1061 for 2, and a = 13.3570(19) Å, b = 13.997(2) Å, c = 17.129(2) Å, α = 67.468(4)°, β = 71.986(5)°, γ = 88.698(6)°, Z = 1, R1 = 0.0461, wR2 = 0.1254 for 3. Three isostructural polyoxotungstates utilize the two-dimensional structures with inorganic–organic composite surfaces built up from tetra-NiII-substituted sandwich-type Keggin polyoxometalate building blocks and NiII-dap cation bridges, representing the first (4,4)-connected topological network in polyoxometalate chemistry. Magnetic susceptibility measurements indicate the occurrence of ferromagnetic coupling interactions within the NiII centers for 1 and 2.
