Two-Dimensional Extended (4,4)-Topological Network Constructed from Tetra-NiII-Substituted Sandwich-Type Keggin Polyoxometalate Building Blocks and NiII-Organic Cation Bridges

Three novel inorganic–organic composite polyoxotungstates {[Ni(dap) 2 (H 2 O)] 2 [Ni(dap) 2 ] 2 [Ni 4 (Hdap) 2 (α-B-HSiW 9 O 34 ) 2 ]}·7H 2 O ( 1 ), {[Ni(dap) 2 (H 2 O)] 2 [Ni(dap) 2 ] 2 [Ni 4 (Hdap) 2 (α-B-HGeW 9 O 34 ) 2 ]}·6H 2 O ( 2 ), and {[Ni(dap) 2 (H 2 O)] 2 [Ni(dap) 2 ] 2 [Ni 4 (Hdap) 2 (α-B-PW 9 O 34 ) 2 ]}·4H 2 O ( 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 P 1̅, 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, R 1 = 0.0742, wR 2 = 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, R 1 = 0.0499, wR 2 = 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, R 1 = 0.0461, wR 2 = 0.1254 for 3 . Three isostructural polyoxotungstates utilize the two-dimensional structures with inorganic–organic composite surfaces built up from tetra-Ni II -substituted sandwich-type Keggin polyoxometalate building blocks and Ni II -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 Ni II centers for 1 and 2 .