The syntheses and structures of the diamagnetic [(DMF)3Mo(O)(mu-S)2Mo(O)(S2)], I, [Ph4p][(C5H5)Mo(O)(mu-S)2Mo(O)(S2)], IV, (Ph4p)2[(S4)Mo(O)(mu-2-S)2Mo(O)(S)], IX, and (Et4N)4{[(S4)Mo(O)(mu-2-S)2Mo(O)(S)]2}, X, complexes are reported. The compounds 1, IV, IX, and X crystallize in the space groups Pcab, P1BAR, P1BAR, and P2(1)/m, respectively. The cell dimensions for I arc as follows: a = 13.152 (3) angstrom, b = 17.554 (5) angstrom, c = 17.893 (5) angstrom, alpha = beta = gamma = 90 and Z = 8; for IV, a = 11.262 (4) angstrom, b = 11.688 (4) angstrom, c = 13.188 (4) angstrom, alpha = 102.11 (2) degrees, beta = 91.73 (3) degrees, gamma = 60.72 (2) degrees, and Z = 2; for IX, a = 10.456 (6) angstrom, b = 12.246 (6) angstrom, c = 19.785 (7) angstrom, alpha = 100.50 (2) degrees, beta = 78.63 (4) degrees, gamma = 84.62 (4) degrees, and Z = 2; and for X, a = 9.261 (2) angstrom, b = 33.909 (8) angstrom, c = 10.082 (2) angstrom, beta = 115.62 (2) degrees, and Z = 2. Crystallographic data for the four structures were obtained on an automatic diffractometer employing Mo K-alpha radiation. The refinement of the structures by full-matrix least-squares methods was based on 1573 unique reflections (2-theta-max = 40-degrees, all data) for 1, on 3180 unique reflections (2-theta-max = 45-degrees, I > 3-sigma-I) for IV, on 4193 unique reflections (2-theta-max 45-degrees, I > 3-sigma-I), for IX, and on 2904 unique reflections (2-theta-max = 45-degrees, I > 3-sigma-I) for X. Anisotropic temperature factors were used for all non-hydrogen atoms in 1, IV, IX, and X. At the current stage of refinement on 208 parameters for I, 343 parameters for IV, 551 parameters for IX, and 286 parameters for X with all atoms present in the asymmetric units, R(w) = 0.039, 0.038, 0.060, and 0.053, respectively. The structures of the complexes in I, IV, and IX contain the [Mo2(mu-2-S)2(O)2]2+ cores with the Mo = O units in the syn configuration. The structure of X is a tetranuclear dimer of IX and contains two fused [(S4)Mo(O)(mu-2-S)2Mo(O)(S)]2- units that share a common MO2O2(mu-2-S)2 unit and are related by a crystallographic mirror plane. The four Mo = O units are all in a syn configuration. Selected structural features for 1, that contains a six-coordinate Mo bound by three facially arranged DMF ligands, include the following: Mo-Mo, 2.813 (1) angstrom; Mo-S(b), 2.317 (3); Mo = O, 1.686 angstrom; Mo-O(DMF)BAR = 2.207 (14) angstrom; Mo-S(b)-Mo, 74.77-degrees; S(b)-Mo-S(b), 102.5-degrees. Selected structural features for IV include the following: Mo-Mo, 2.855 (1) angstrom; Mo-S(b), 2.310 (4); Mo = O, 1.673 angstrom; Mo-CBAR(cp) = 2.380 (9) angstrom; Mo-S(b)-Mo, 76.32-degrees; S(b)-Mo-Sb, 101.3-degrees. The Mo-Mo distance in IX is found at 2.896 (1) angstrom. In X, the Mo-Mo distance of the outer Mo-(mu-2-S)2-Mo units at 2.852 (2) angstrom is shorter than the Mo-Mo distance in the central Mo-(mu-2-S)2-Mo unit at 3.554 (2) angstrom. The long Mo-S(b) bond in the central Mo-(mu-2-S)2-Mo unit in X at 2.420 angstrom by comparison to the Mo-S(b) bonds in the outer Mo-(mu-2-S)2-Mo unit in X (2.337 angstrom), or the same unit in IX, (2.325 angstrom) underscore the weak nature of the central Mo-(mu-2-S)2-Mo unit in X. Consistent with the crystallographic results is the solution behavior of IX and X that shows dimer-tetramer equilibria for these complexes. The reaction of IV with Ph3p affords the [(C5H5)Mo(O)(mu-S)2Mo(O)(S)]- anion that in solution exists in equilibrium with the {[(C5H5)Mo(O)(mu-S)2Mo(O)(S2)]2}2- tetramer. In DMF solution, at 310 K, K(eq) = 1 x 10(-3). The reactions of the Mo = S chromophores, in the Mo(O)(S) units of these complexes and their derivatives, with dicarbomethoxyacetylene and CS2 are described. The possible significance of an active Mo = S functional group in enzymatic oxotransferase reactions and in the industrially important hydrodesulfurization reaction is discussed.
