Herein we report the synthesis, X-ray structure, and characterization of the title pentairon (molybdo)carbido cluster. The reaction of the pentairon (mu(s)-carbido) dianion [Fe-5(mu(6)-C)(mu(2)-CO)(2) (CO)(12)](2-) (1) with [Mo(CO)(3)(chpt)] (chpt = cycloheptatriene) forms the heterohexanuclear cluster [K(benzo-18-crown-6)](2)[Fe5Mo(mu(6)-C)(mu(2)-CO)(3)(CO)(14)] (2). The dianion exhibits a Fe5Mo(mu(6)-C) core structure supported by three bridging (v(co) = 1788 cm(-1)) and terminal (v(co) = 1943 cm(-1)) CO ligands. Cluster 2 provides the selective reduction of diphenylacetylene to cis-diphenylethylene via a spectroscopically observed cluster-hydride intermediate (H-1 NMR: delta-26).