The product of insertion MoCl4{[N(Et)C(S)]2Cl} (I) was obtained by reacting MoCl5 with EtNCS in dichloroethane. The hydrolysis of this complex gave single crystals of (NH3Et)[MoOCl4(H2O)] (II), which were characterized by X-ray crystallography. The crystals of II consist of complex anions [MoVOCl4(H2O)]- and ethylammonium cations united by an extended network of interionic contacts N-H⋯Cl, N-H⋯O, and C-H⋯O. The bond lengths in the coordination octahedron MoO2Cl4: Mo=O(oxo), 1.67 Å; Mo-O(H2O)trans, 2,381 Å, and Mo-Clcis, 2.365 Å. On the basis of the X-ray diffraction data, the assignment of the frequencies in the IR spectra of II was performed. The results of the X-ray diffraction study and IR spectroscopy for I allowed us to conclude that the addition of ethyl isothiocyanate to pentachloromolybdenum(V) is stereospecific.