The novel ternary reduced molybdenum oxide Mnsimilar to2.4Mo6O9 has been synthesized by solid-state reaction at 1400 degreesC for 96 h in sealed molybdenum crucibles. Electron diffraction studies showed that Mnsimilar to2.4Mo6O9 presents a complex crystal structure with a 3d incommensurate modulation. The average crystal structure was determined on a single-crystal by X-ray diffraction in the orthorhombic space group Pnma with the following lattice parameters: a = 16,4824(2) Angstrom, b = 2.8273(2) Angstrom, c = 17.3283(2) Angstrom, Z = 4. The Mo network consists of empty twin chains of trans-edge-sharing octahedra that occur for the first time in a solid-state compound. The Mo-Mo distances within the chains range from 2.62 to 2.92 Angstrom, and the Mo-O distances from 1.99 to 2.17 Angstrom as usually observed in the reduced molybdenum oxides. Single-crystal resistivity measurements show that Mnsimilar to2.4Mo6O9 is metallic between 4.2 and 300 K. The magnetic susceptibility data indicate paramagnetic behavior due to the Mn2+ moment at high temperatures with a weak ferromagnetic behavior below 80 K.