The novel quaternary reduced molybdenum oxides MTi0.7Mo0.3Mo5O10 (M = Sr, Eu) have been synthesized by solid-state reaction at 1400 degreesC for 48 h in sealed molybdenum crucibles. Their crystal structures were determined on single crystals by X-ray diffraction. Both compounds crystallize in the orthorhombic space group Pbca with 8 formula units per cell and the following lattice parameters: a(Sr) = 9.1085 (7), b(Sr) = 11.418 (1), and c(Sr) = 15.092 (3) Angstrom; a(Eu) = 9.1069 (7), b(Eu) = 11.421 (2), and c(Eu) = 15.075 (1) Angstrom. The Mo network is dominated by bioctahedral Mole clusters, which coexist randomly with Mo-11 and Mo-12 clusters (monocapped and bicapped Mole clusters). The Mo-Mo distances within the clusters range from 2.62 to 2.92 Angstrom and the Mo-O distances from 1.99 to 2.17 8,as usually observed in the reduced molybdenum oxides. The Sr2+ and Eu2+ ions occupy large cavities, which result from the fusion of two cubooctahedra and thus are surrounded by 11 oxygen atoms. The M-O distances range from 2.50 to 3.23 Angstrom for the Sr compound and from 2.49 to 3.24 Angstrom for the Eu analogue. Single-crystal resistivity measurements indicate that both materials are poor metals with transitions to semiconducting states below 50 and 40 K and room temperature resistivity values of 9 x 10(-3) and 5 x 10(-3) Omega. cm for the Sr and Eu compounds, respectively. The magnetic susceptibility data indicate paramagnetic behavior due to the Eu2+ moment at high temperatures for the Eu compound and do not reveal the existence of localized moments on the Mo and Ti sublattice in the Sr compound. An XPS study clearly suggests that the isolated Ti ions are tetravalent. Theoretical considerations preclude the existence of heterometallic Mo-Ti clusters.