Ionothermal syntheses of three transition-metal-containing polyoxotungstate hybrids exhibiting the photocatalytic and electrocatalytic properties

Abstract

Employing the ionothermal synthesis approach, three new transition-metal-containing polyoxotungstate hybrids: [Dmim] 2Na 3[SiW 11O 39Fe(H 2O)]·H 2O (Dmim=1,3-Dimethylimidazole) ( 1), [Emim] 9Na 8[(SiW 9O 34) 3{Fe 3(μ 2-OH) 2(μ 3-O)} 3(WO 4)]·0.5H 2O(Emim=1-Ethyl-3-meth-ylimidazole) ( 2) and [Dmim]2[HMim]Na 6[(AsW 9O 33) 2{Mn III(H 2O)} 3]·3H 2O (Dmim=1,3-Dimethylimidazole; Mim=1-Methylimidazole) ( 3) have been synthesized in 1-ethyl-3-methyl imidazolium bromide ([Emim]Br) ionic liquids (ILs). Compound 1 possesses a 3-D open framework constructed from the mono-iron III-substituted α-Keggin-type anion and the organic cations [Dmim]+ through the hydrogen bond interactions. Compound 2 contains a [{Fe III 3(μ 2-OH) 2(μ 3-O)} 3(μ 4-WO 4)] cluster surrounded by three [SiW 9O 34] 10− ligands, eight sodium cations and nine dissociative [Emim] + cations around the polyoxoanion. The polyoxoanion of 3 consists of a high-valent trinuclear-manganese (III)-substituted sandwiching polyoxoanion based on the [α-AsW 9O 33] 9− units. All the compounds are characterized by elemental analyses, IR, UV–vis spectra, TG-DTA and XRD analyses. The XPS and EPR spectra of Mn III in 3 were studied. The photocatalytic and electrocatalytic properties, as well as the stabilities of 1– 3 were also investigated.