The aluminum trichloride/l-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)Cl-18](5-) from the solid state precursor Rb5Zr6Cl18B. Im(5)Zr(6)Cl(18)B . C6H5CH3 . 2CH(3)CN 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) Angstrom, b = 17.256(3) Angstrom, c = 23.295(5) Angstrom, beta = 104.68(2)degrees, and Z = 4. One of the crystallographically independent 1-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)Cl-18](5-) cluster and the oxidized 13 e [(Zr6B)Cl-18](4-) cluster were recorded. B-11 NMR solution spectra of [(Zr6B)Cl-18](5-) 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 handline, 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.