Solvent-mediated purification of hexa-molybdenum cluster halide, Cs2[Mo6Cl14] for enhanced optical properties

The crystallization of a high-purity hexamolybdenum cluster chloride, Cs2[Mo6Cl14], was investigated with the aim of improving its intrinsic properties, including optical properties. In particular, we used the hydrophilicities of alcoholic solvents to purify Cs2[Mo6Cl14] by dehydration. The precursor, trigonal Cs2[Mo6Cl14] with water impurities, or monoclinic Cs2[Mo6Cl14]·H2O, was dispersed in methanol (MeOH), ethanol (EtOH), or 1-propanol (1-PrOH) to induce recrystallization during stirring. As a result, regardless of the precursor, Cs2[Mo6Cl14] crystallized from EtOH and 1-PrOH, while Cs2[Mo6Cl14]·H2O crystallized from MeOH, which indicates that EtOH and 1-PrOH behave as dehydrating agents during recrystallization. Subsequent characterization by X-ray diffraction, thermal desorption, and infrared spectroscopic techniques confirmed that the Cs2[Mo6Cl14] crystallized from EtOH or 1-PrOH, particularly 1-PrOH, is of high purity (fewer inserted water molecules) and high crystallinity. Improved luminescence efficiency following purification was evidenced by time-resolved photoluminescence measurements; the Cs2[Mo6Cl14] purified by dehydration on recrystallization clearly exhibited an increased luminescence lifetime.