Combination of lacunary polyoxometalates and high-nuclear transition metal clusters under hydrothermal conditions: IX. a series of novel polyoxotungstates sandwiched by octa-copper clusters

The reaction of CuCl(2).2 H2O with trivacant Keggin polyoxoanions K8Na2A-alpha-GeW9O34].25 H2O or K10A-alpha-SiW9O34].25 H2O in the presence of 1,2-diaminopropane (dap), ethylenediamine (en) or 2,2'-bipyridine (2,2'-bpy) under hydrothermal conditions afforded five novel hybrid inorganic-organic octa-Cu sandwiched polyoxotungstates (POTs): H4CuII8(dap)4(H2O)2(B-alpha-GeW9O34)2].13 H2O (1), (H2en)2CuII8-(en)4(H2O)2(B-alpha-GeW9O34)2].5 H2O(2), (H2en)2CuII8(en)4(H2O)2(B-alpha-SiW9-O34)2].8 H2O (3), CuII(H2O)2]H2CuII8-(en)4(H2O)2(B-alpha-SiW9O34)2] (4), and CuII2(H2O)2(2,2'-bpy)2]{CuII(bdyl)]2-CuII8(2,2'-bpy)4(H2O)2(B-alpha-GeW9-O34)2]}.4 H2O (bdyl=2,2'-bipyridinyl)(5). Additionally, CuCl(2).2 H2O reacts with the mixture of GeO2, Na2WO(4).2 H2O, H2SiW12O(40).2 H2O in the presence of 2,2'-bpy and 4,4'-bpy under hydrothermal conditions leading to another novel mixed-valent octa-Cu sandwiched POT hybrid: CuI(2,2'-bpy)(4,4'-bpy)]2{CuI2(2,2'-bpy)2(4,4'-bpy)]2CuI2CuII6(2,2'-bpy)2(4,4'-bpy)2(B-alpha-GeW9O34)2}].2 H2O (6). 1, 2, and 3 are discrete dimers constructed from two trivacant Keggin B-alpha-XW9O34]10- (X=GeIV/SiIV) fragments and an octa-Cu cluster whereas 4 displays the 3D (3,6)-connected nets with (4.6(2))(4(2).6(4).8(7).10(2)) topology, which are built by octa-Cu sandwiched polyoxometalate building blocks through copper cation bridges. 5 is a novel 2D layer based on octa-Cu sandwiched POT clusters and CuII2(bdyl)] units. Interestingly, the rollover metalation of 2,2'-bpy is firstly observed in the system containing the copper complex under hydrothermal conditions. 6 is a discrete mixed-valent octa-Cu sandwiched POT supported by two CuI-complexes CuI2-(2,2'-bpy)2(4,4'-bpy)]2+ through 4,4'-bpy bridges, which constructs a novel dodeca-copper cluster. Notably, the octa-Cu cluster in 6 is mixed-valent and is different from those in 1-5. To our knowledge, 1-6 represent a rare family of POTs incorporating novel octa-nuclear transition-metal clusters in polyoxometalate chemistry. They were structurally characterized by FT-IR spectra, elemental analysis, thermogravimetric analysis, and single-crystal X-ray diffraction. The magnetic properties of 1, 4, and 5 were quantitatively analyzed by the MAGPACK software package.