’A series of new complexes, Mo2O2S2[S2P(OR)(2)](2) (where R = Et, n-Pr, i-Pr) and Mo2O2S2[S(2)POGO](2) (where G = -CH(2)CMe(2)CH(2)-, -CMe(2)CMe(2)-) have been prepared by the dropwise addition of an ethanolic solution of the ammonium or sodium salt of the appropriate O,O-dialkyl or -alkylene dithiophosphoric acid, or the acid itself, to a hot aqueous solution of molybdenum(V) pentachloride. The complexes were also formed by heating solutions of Mo2O3[S2P(OR)(2)](4) or Mo2O3[S(2)POGO](4) species in glacial acetic acid. The Mo2O2S2[S2P(OR)(2)](2) and Mo2O2S2[S(2)POGO](2) compounds were characterized by elemental analyses, H-1, C-13, and P-31 NMR, and infrared and Raman spectroscopy, as were the 1:2 adducts formed on reaction with pyridine. The crystal structures of Mo2O2S2[S2P(OEt(2))](2), Mo2O2S2[S2P(OEt)(2)](2) . 2NC(5)H(5), and Mo2O3[S2P(OPh)(2)](4) were determined. Mo2O2S2[S2P(OEt)(2)](2) (1) crystallizes in space group C2/c, No. 15, with cell parameters a = 15.644(3) Angstrom, b = 8.339(2) Angstrom, c = 18.269(4) Angstrom, beta = 103.70(2)degrees, V = 2315.4(8) Angstrom(3), Z = 4, R = 0.0439, and R(w) = 0.0353. Mo2O2S2[S2P (OEt)(2)](2) . 2NC(5)H(5) (6) crystallizes in space group , No. 2, with the cell parameters a = 12.663(4) Angstrom, b = 14.291(5) Angstrom, c = 9.349(3) Angstrom, alpha = 100.04(3)degrees, beta = 100.67(3)degrees, gamma = 73.03(3)degrees V = 1557(1) Angstrom(3), Z = 2, R = 0.0593, and R(w) = 0.0535. Mo2O3[S2P(OPh)(2)](4) (8) crystallizes in space group P2(1)/n, No. 14, with cell parameters a = 15.206(2) Angstrom, b = 10.655(3) Angstrom, c = 19.406(3) Angstrom, beta = 111.67(1)degrees, V = 2921(1) Angstrom(3), Z = 2, R = 0.0518, R(w) = 0.0425. The immediate environment about the molybdenum atoms in 1 is essentially square pyramidal if the Mo-Mo interaction is ignored. The vacant positions in the square pyramids are occupied by two pyridine molecules in 6, resulting in an octahedral environment with very long Mo-N bonds. The terminal oxygen atoms in both 1 and 6 are in the syn conformation. In 8, which also has a distorted octahedral environment about molybdenum, two of the dithiophosphate groups are bidentate as in 1 and 6, but the two others have one normal Mo-S bond and one unusually long Mo-S bond.