Both Rigid Organic Ligands and pH-Controlled Three Keggin-Type Polyoxotungstates Derivates: Synthesis, Crystal Structure

Three Keggin polyoxotungstate inorganic–organic hybrid compounds have been synthesized under hydrothermal conditions by using H 4 SiW 12 O 40 as starting materials: [{Cu II (2,2′-bipy) 2 } 2 SiW 12 O 40 ]·2H 2 O ( 1 ), [{Cu II (phen) 2 } 2 SiW 12 O 40 ] ( 2 ) and [{Cu I (2,2′-bipy) 2 } 4 SiW 12 O 40 ] ( 3 ) (2,2′-bipy = 2,2′-bipyridine, phen = 1,10′-phenanthroline) and structurally characterized by elemental analysis, IR spectra, TG analysis and X-ray single-crystal diffraction. Three compounds are all based on [SiW 12 O 40 ] 4− α-Keggin type building block and synthesized under the same reaction condition, only different compound 1 and 2 ligand, 1 and 3 pH value. Compound 1 displays a novel example of two-dimensional framework with tetra-supporting α-Keggin polyanions which are linked by four same fragments and it becomes 3D structure due to the existence of hydrogen bonds. Compound 2 shows that the bi-supporting polyoxotungstate molecule consists of a α-Keggin polyoxoanion [SiW 12 O 40 ] 4− and a pair of transition metal complex fragments which are covalently linked to opposite sides of the surface terminal oxygen atoms of WO 6 octahedra. Compound 3 consists of α-[SiW 12 O 40 ] 4− polyoxoanions, counter cations [Cu(2,2′-bipy) 2 ] + . The crystal packing is stabilized by H-bonds and weak π–π interactions, leads to a 3D supramolecular architecture. The results show that the pH value of the reaction system plays a crucial role in structural control of self-assembled processes. The thermal stabilities of the compounds are discussed. Graphical Abstract Three Keggin polyoxotungstate inorganic–organic hybrid compounds have been synthesized under hydrothermal conditions by using H 4 SiW 12 O 40 as starting materials: [{Cu II (2,2′-bipy) 2 } 2 SiW 12 O 40 ]·2H 2 O ( 1 ), [{Cu II (phen) 2 } 2 SiW 12 O 40 ] ( 2 ) and [{Cu I (2,2′-bipy) 2 } 4 SiW 12 O 40 ] ( 3 ) (2,2′-bipy = 2,2′-bipyridine, phen = 1,10′-phenanthroline) and structurally characterized by elemental analysis, IR spectra, TG analysis and X-ray single-crystal diffraction. Three compounds are all based on [SiW 12 O 40 ] 4− α-Keggin type building block and synthesized under the same reaction condition, only different compound 1 and 2 ligand, 1 and 3 pH value.