Bis(oxodialkyldithiocarbamato)molybdenum(VI) complexes react with concentrated hydrohalogenic acids to yield the novel compounds [MoOX2(S2CNR2)2](where X = F, Cl, or Br; R = Me, Et, or Prn). The crystal structure of the complex (I)[MoOCl2(S2CNEt2)2] confirms that the compounds are seven-co-ordinate. Crystals are monoclinic, space group P21/C with a= 8.900(2), b= 17.500(4), c= 12.703(3)Å, β= 110.16(3)°. The structure was refined to R 0.040 by use of 2 350 independent reflections measured by diffractometer. In order to establish the generality of the cis-mer configuration, the structure of the compound (II)[MoOBr2(S2CNEt2)2] was also studies. Crystals are triclinic, space group P, with a= 9.952(3), b= 13.974(5), c= 7.548(3)Å, α= 75.69(3), β= 108.23(3), γ= 99.70(3)°. Its geometry is essentially the same as that of (I) and its structure was refined to R 0.056 by use of 3 081 independent reflections. I.r. and far-i.r. spectra are discussed.