A soft and convenient single step route is developed to synthesize molybdenum cluster compounds using an ionic liquid as reaction medium. Bi[Mo5Cl13]Cl and [BiCl][Mo6Cl14] were isolated from the ionic liquid [BMIM]Cl/AlCl3 ([BMIM]+: 1-n-butyl-3-methylimidazolium) and characterized. Black, cubic crystals of Bi[Mo5Cl13]Cl are obtained at room temperature by the reaction of bismuth, BiCl3, and MoCl5 in Lewis-acidic ionic liquid [BMIM]Cl/AlCl3. Bi[Mo5Cl13]Cl crystallizes in the cubic space group Pn with a = 1291.6(3) pm. In the [Mo5Cl13]2– cluster, the molybdenum atoms form a square pyramid with Mo–Mo bond lengths 258.9(2) pm and 259.5(2) pm. The structure is a defect variant of the Pb[Mo6Cl14] type; in statistical distribution one of the molybdenum atoms is missing in the cluster core. The bismuth(III) cations, which are in octahedral coordination by the apical chloride ions of the clusters, connect the cluster anions into a three dimensional network. Light red crystals of monoclinic [BiCl][Mo6Cl14] were obtained by the oxidation of bismuth with MoCl5 in [BMIM]Cl/AlCl3. The structure determination is in excellent agreement with literature data of crystals obtained by high temperature syntheses.