Abstract
A Zn,Al layered double hydroxide (LDH) with [Cp*MoO3]– (Cp* = η5‐C5Me5) anions in the interlayer has been prepared by a direct coprecipitation method. The intercalated LDH and the mixed metal oxide (MMO) obtained after its calcination were characterized by elemental and thermogravimetric analyses, powder X‐ray diffraction (PXRD), FT‐IR and FT‐Raman spectroscopy, 13C and 27Al MAS NMR, and scanning electron microscopy. The observed basal spacing of 17.1 Å for the LDH Zn,Al‐Cp*MoO3 (corresponding to a gallery height of 12.3 Å) suggests that the guest anions self‐assemble into dimers via offset face‐to‐face Cp*···Cp* interactions, which facilitates hydrogen‐bonding interactions between the oxido ligands of the complexes and the layer hydroxyl groups, while positioning the hydrophobic aromatic rings towards the center of the galleries. Calcination of Zn,Al‐Cp*MoO3 at 550 °C under air gave an MMO comprising well‐dispersed ZnO, α‐ZnMoO4 and ZnAl2O4 (spinel) oxides in a molar of ca. 1.4:1.6:1. The MMO exhibited catalytic activity for the epoxidation of cis‐cyclooctene with tert‐butylhydroperoxide (TBHP) as terminal oxidant, with quantitative yield of the epoxide being achieved within 24 h at 85 °C.
Highlights
The intercalation of atomic or molecular guest species into lamellar inorganic crystals has been explored since the 1970s as a means to engineer complex organized structures at the nanoscale.[1,2,3,4,5] Intercalation can modify the physical and chemical properties of the host and guest, leading to new materials with optical, optoelectronic, conductive, energy storage, and catalytic applications, among others
In this paper we report the direct self-assembly synthesis of an expanded layered double hydroxide (LDH) intercalated phase containing the trioxido anion [Cp*MoO3]– (Cp* = 5-C5Me5)
The ion exchange approach, using a Zn,AlNO3 precursor and excess Na[Cp*MoO3] dissolved in either water or a THF/MeOH mixture, did not lead to any significant intercalation after stirring the mixture at 50 °C for two days, as evidenced by FT-IR spectroscopy and powder X-ray diffraction (PXRD). This method was abandoned and the direct coprecipitation method was pursued, which has previously been used to prepare LDHs intercalated by ferrocene(di)carboxylate anions[22] and the halfsandwich complex [CpMo(CO)3CH2COO–].[29]
Summary
The intercalation of atomic or molecular guest species into lamellar inorganic crystals has been explored since the 1970s as a means to engineer complex organized structures at the nanoscale.[1,2,3,4,5] Intercalation can modify the physical and chemical properties of the host and guest, leading to new materials with optical, optoelectronic, conductive, energy storage, and catalytic applications, among others. There are few reports of the incorporation of half-sandwich “piano stool” complexes within inorganic layered materials, with two examples being [CpRu(benzo-15-crown-5)]+ in MPS3 (M = Mn, Cd, Zn),[28] and [CpMo(CO)3CH2COO–] in a Zn,Al LDH.[29]
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