Extraction and Isolation of the [(Zr6B)Cl18]5- Cluster from a Solid State Precursor
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The aluminum trichloride/1-ethyl-3-methylimidazolium chloride (ImCl/AlCl3) room-temperature ionic liquid is used in the extraction and isolation of the unoxidized B-centered zirconium cluster [(Zr6B)Cl18]5 from the solid state precursor Rb5Zr6Cl18B. Im5Zr6Cl18BC6H5CH32CH3CN was crystallized by diffusion of an ImCl/AlCl3-CH3CN solution of the cluster into toluene at ambient temperature. It crystallizes in the space group C2/c (No. 15) with a = 18.415(4) , b = 17.256(3) , c = 23.295(5) , = 104.68(2), and Z = 4. One of the crystallographically independent l-ethyl-3-methylimidazolium cations is severely disordered, though an adequate model was found to accommodate it. UV-visible-near IR spectra of both the unoxidized 14 e [(Zr6B)Cl18]5 cluster and the oxidized 13 e [(Zr6B)Cl18]4 cluster were recorded. 11B NMR solution spectra of [(Zr6B)Cl18]5 in both ImCl/AlCl3 and CH3CN and the solid state spectrum of Rb5Zr6Cl18B were measured. The very low field chemical shifts (184 ppm in ImCl/AlCl3) and the narrow line widths are characteristic of the unoxidized 14 e octahedral boron-centered zirconium clusters in solution and the solid state. With proper handling, the previously observed cluster oxidation can be avoided during dissolution of Rb5Zr6Cl18B in either ImCl/AlCl3 or CH3CN. Additional experimentation implicates impurities in added organic chloride salts as the likely oxidants in previous investigations. 1995, American Chemical Society. All rights reserved.
