The title compound forms black crystals shaped like pseudo-octahedrons, which belong to the orthorhombic system The space group is Pna 2_1 with unit cell parametrs of a=17.815(1), b=16.629(2), c=12.003(1), and with Z=4, D_(obs)=1.80g·cm~(-3), and D_(calc)=1.804g·cm~(-3). The crystal structure was solved by the heavy atom method and refiened by fullmatrix least-squares to a final conventional R factor of 0.048 for 2584 unique reflections with I≥σ(Ⅰ). The investigation confirms that the crystal structure consists of tetraethylammonium cations and trinuclear Mo cluster anions. The anion is a μ_3-O monocapped trinuclear cluster with an average Mo-Mo bond length of 2.60 (2). On the side of the Mo_3 triangular plane opposite to the μ_3-O atom, each two Mo atoms are bridged by a Cl atom with the result that these seven atoms (3 Me, 1 O and 3 Cl atoms)form an apex-deficient quasicubane configuration. In addition, each Mo atom is coordinated to three additional atoms resulting in a pseudo-octahedral geome The title compound forms of black crystalline form like pseudo-octahedrons, which belong to the orthorhombic system The space group is Pna 2_1 with unit cell parametrs of a = 17.815 (1), b = 16.629 (2), c = 12.003 and with Z = 4, D obs = 1.80g · cm -3, and D calc = 1.804g · cm -3 The crystal structure was solved by the heavy atom method and refiened by fullmatrix least-squares to a final conventional R factor of 0.048 for 2584 unique reflections with I≥σ (I). The investigation confirms that the crystal structure consists of tetraethylammonium cations and trinuclear Mo cluster anions. The anion is a μ_3-O monocapped trinuclear cluster with an average Mo-Mo bond length of 2.60 (2). On the side of the Mo_3 triangular plane opposite to the μ_3-O atom, each two Mo atoms are bridged by a Cl atom with the result that these seven atoms Me, 1 O and 3 Cl atoms) form an apex-deficient quasicubane configuration. In addition, each Mo atom is coordinated to three additional atoms resulting in a pse udo-octahedral geome