Heterobimetallic Alkoxides [Cd^IIM^V(OiPr)₇]₂ (M = Nb, Ta) as Potential Precursors to Pyrochlore Cd₂M₂O₇

Abstract

Attempts to synthesize Cd-M (M = Nb, Ta) heterobimetallic complexes by salt metathesis reaction resulted in the unexpected structural motif [I 2 Cd II 2 M V (OiPr) 7 ] 2 [M = Nb (2), Ta (3)]. Multinuclear NMR analysis revealed the coexistence of multiple products in solution. Donor solvents influenced the formation of different intermediate species in solution, as was proven by 113 Cd NMR spectroscopic data. The isolation of trimetallic [I 2 Cd{Ta(OiPr) 6 }K(HOiPr) 2 ] 4 (4) and the adduct [I 2 CdTa(OiPr) 5 -(thf )] (5) provided insight into the reaction mechanism. By exploiting the Lewis acidic nature of cadmium alkoxides, different compounds could be synthesized and thoroughly characterized [a] General Procedures: All syntheses were performed under an inert nitrogen atmosphere by using a modified Stock glass vacuum line. The solvents were dried with and distilled from sodium benzophenone and stored over molecular sieves. CdI 2 (98 %) was used as purchased from ACROS chemicals. NbCl 5 and TaCl 5 were purchased from abcr Chemicals in a purity of 98 % and used as received. The precursors [Cd{N(Si(Me) 3 ) 2 } 2 ], [20] [Nb 2 (OiPr) 10 ], [23] and [Ta 2 (OiPr) 10 ] [23] were synthesized according to previously described procedures. The 1 H, 113 Cd, 13 C, and 93 Nb NMR spectra were recorded with a Bruker AVANCE II 300 spectrometer and are referenced to SiMe 4 ( 1 H, 300.0 MHz; 13 C, 75.4 MHz), CdMe 2 50 % v/v in CDCl 3 ( 113 Cd, 66.0 MHz), and KNbCl 6 ( 93 Nb, 73.46 MHz), respectively. Microanalysis for C, H, N, and S was carried out with a Hekatech CHNS EuroEA 3000 analyzer with helium as carrier gas. The discrepancy between calculated and measured values can be attributed to the high moisture sensitivity of the compounds. TG/DTA measurements were performed with a Mettler TGA/DSC 1 STAR system with a GC 100 gas controller. Samples were put in an aluminum cartridge (HEKAtech GmbH, 5 × 12 mm) and sealed, and measurements were performed under a 25 mL min -1 N 2 flow between 40 and 630°C with a heating rate of 10°C min -1 . In situ high-temperature X-ray diffraction data were collected with a STOE Stadi-P System equipped with a hightemperature unit and an image-plate detector by using Cu-K α 1 (0.15418 nm) radiation. Before data collection the solid precursor was transferred under inert conditions into a quartz capillary in a glove box. The sample was heated in steps of 100°C from room temp. to 600°C. The exposure time for each step was 1 h. Raw data were handled with the STOE WinXPOW Software. Data collections for X-ray crystal structure determination for compounds 2-7 were performed with a STOE IPDS 2 T diffractometer by using graphitemonochromated Mo-K α radiation (λ = 0.71073 Å). The data were corrected for Lorentzian and polarization effects. A numerical absorption correction based on crystal-shape optimization was applied for all data. [23] The programs used for structure solution and refinement include SIR92, [24] SHELXS, [25] SHELXL, [25] and WinGX. [19,26] Eur.

Molecularly Engineered Lithium–Chromium Alkoxide for Selective Synthesis of LiCrO2 and Li2CrO4 Nanomaterials

“…: 53.58%), possibly due to partial hydrolysis during the sample preparation. facilitate the crystallization of materials at relatively lower temperature when compared to solid-state synthesis [20][21][22]. We demonstrate here, for the first time, the influence of molecular-level processing in the controlled synthesis of LiCrO2 nanomaterials with stoichiometry control between the heterometallic precursors and the resulting mixed oxide ceramics, which is rather difficult in preparation with the solid-state or multi-source precursor approach.…”

“…To our best knowledge, there is no report on the preparation of stoichiometric LiCrO 2 nanomaterials from molecular single-source precursors [17][18][19]. The pre-existent chemical bonds between the phase-forming elements in molecular precursors can facilitate the crystallization of materials at relatively lower temperature when compared to solid-state synthesis [20][21][22].…”