Polycrystalline samples and single crystals of the R 4 Mo 4 O 11 compounds (R ΒΌ Yb and Lu) were synthesized by solid-state reactions at high temperature in sealed Mo crucibles. The structure of Lu 4 Mo 4 O 11 (a ΒΌ 10.5611(1), b ΒΌ 5.61930(5), c ΒΌ 15.6877 (2), b ΒΌ 99.5131(4) and Z ΒΌ 4) was determined by single crystal X-ray diffraction and refined by least squares on F 2 converging to R 1 ΒΌ 0.0425, wR 2 ΒΌ 0.0980 for 3508 intensities. Contrary to the R 4 Mo 4 O 11 compounds with lighter rare earths, which crystallize in the orthorhombic space group Pbam, the Yb and Lu compounds crystallize in the monoclinic space group P2/m. The R 4 Mo 4 O 11 compounds contain distorted infinite oxide-molybdenum chains of trans-edge-sharing Mo 6 octahedra diluted with the rare earths. Magnetic susceptibility measurements indicate that the oxidation state of the Yb atoms is +3, affording 14 metallic valence electrons per Mo 4 fragment and, the absence of localized moments on the Mo network. Resistivity measurements on single crystals show that the Yb 4 Mo 4 O 11 and Lu 4 Mo 4 O 11 compounds are small band-gap semi-conductors.