pH-dependent assembly of 0D to 3D Keggin-based coordination polymers: Structures and catalytic properties

Abstract

Four Keggin-based coordination polymers, namely, {[Cu2(4,4'-bpy)(4,4'-Hbpy)4(H2O)4](SiW12O40)2(H2O)4}n (1), {[Cu2(4,4'-bpy)(4,4'-Hbpy)6(SiW12O40)3](4,4'-Hbpy)2(H2O)7}n (2), {[Cu2(mu2-H2O)2(4,4'-bpy)3(SiW12O40)](H2O)6}n (3) and {[Cu2(mu2-OH)(4,4'-bpy)3(SiW12O40)(H2O)] [Cu2(mu2-O)(4,4'-bpy)4(H2O)2]0.5 x (H2O)3}n (4) (4,4'-bpy = 4,4'-bipyridine) were prepared through the hydrothermal reaction of silicotungstic acid, copper(II) nitrate and 4,4'-bipyridine under different pH conditions. Coordination polymers 1 and 2, which exhibit 0D and 1D structures respectively, were prepared at pH = 3.5. At pH = 5.5, a 2D coordination polymer 3 was obtained. Increasing the pH of the reaction to 8.5 led to a 3D coordination polymer 4. The structural diversities of 1-4 reveal that the pH value of the reaction plays a key role in the assembly of POM-based coordination polymers. Investigation of the catalytic properties of 1-4 for the oxidation of ethylbenzene indicates that the catalytic activity of the coordination polymers is closely related to the protonated extent of 4,4'-bpy in the coordination polymers.

Heterogeneous Catalysis of Polyoxometalate Based Organic–Inorganic Hybrids

“…Long et al reported the synthesis of four organic–inorganic hybrid POM compounds, {[Cu 2 (4,4'-bpy)(4,4'-Hbpy) 4 (H 2 O) 4 ](SiW 12 O 40 ) 2 (H 2 O) 4 } n ( 1 ), {[Cu 2 (4,4'-bpy)(4,4'-Hbpy) 6 (SiW 12 O 40 ) 3 ](4,4'-Hbpy) 2 (H 2 O) 7 } n ( 2 ), {[Cu 2 (μ 2 -H 2 O) 2 (4,4'-bpy) 3 (SiW 12 O 40 )](H 2 O) 6 } n ( 3 ), {[Cu 2 (μ 2 -OH)(4,4'-bpy) 3 (SiW 12 O 40 )(H 2 O)][Cu 2 (μ 2 -O)(4,4'-bpy) 4 (H 2 O) 2 ] 0.5 (H 2 O) 3 } n ( 4 ), by reaction of Keggin-type [SiW 12 O 40 ] 4− polyoxoanion, Cu ion, and 4,4'-bpy under hydrothermal conditions [44]. The Cu ions and 4,4'-bpy molecules are connected to form four different types of dinuclear copper coordination cations under different pH conditions.…”

“…Long et al reported the catalytic results of epoxidation of styrene over four {SiW 12 }-based compounds 1 – 4 with TBHP as oxidant. The compounds showed high catalytic activity but the main product was benzaldehyde [44]. The distribution of the products indicated that the reaction was acid sensitive.…”

Lanthanide coordination compounds with 2,2′-bipyridine-6,6′-dicarboxylate: Synthesis, crystal structure, luminescence and magnetic property

“…Their structures change from zero dimension to two dimension with chelating and bridging coordination modes. But there have been few systematic studies on the influence of the pH values of the reaction system on structures, and by tuning the pH values, the structures of the final compounds could be regulated [28][29][30][31][32][33][34][35][36]. A number of reasons that the pH values regulated the structures have reported, such as influencing the deprotonated extend of ligands [34,37], facilitating the formation of l-OH group [29], generating different conformations and coordination modes [38].…”

Three POM-based coordination polymers: hydrothermal synthesis, characterization, and catalytic activity in epoxidation of styrene

“…Recently, investigation on their catalytic activity has begun to attract attention. 7 The selection of organic ligand is crucial in the design and synthesis of POM-based coordination polymers. The properties of organic ligands, such as length, geometry, coordination ability and relative orientation of the donor groups play important roles in generating framework topology.…”