| Abstract
| - Studies on the solution chemistry of the singleand double cuboidal clusters[Mo3SnS4(H2O)12]6+and[Mo6SnS8(H2O)18]8+are described. The crystal structure of the dimethylammonium saltof[Mo3(SnCl3)S4(NCS)9]6-has been determined. The tin atom of the single cube has a highaffinity for Cl- and, in the case of the double cube,Cl- initiates a breakdown to the single cube and[Mo3S4(H2O)9]4+.High-yield redox-induced interconversions of the double and singlecubes have been achieved. Thermodynamic and kinetic data arepresented.
- The Mo3SnS46+ singlecube is obtained by direct addition of Sn2+ to[Mo3S4(H2O)9]4+.UV−vis spectra of theproduct (0.13 mM) in 2.00 M HClO4, Hpts, and HCl indicate amarked affinity of the Sn for Cl-, withformationof the more strongly yellow[Mo3(SnCl3)S4(H2O)9]3+complex complete in as little as 0.050 M Cl-. TheX-raycrystal structure of(Me2NH2)6[Mo3(SnCl3)S4(NCS)9]·0.5H2Ohas been determined and gives Mo−Mo (mean2.730 Å) and Mo−Sn (mean 3.732 Å) distances, with a differenceclose to 1 Å. The red-purple double cubecation[Mo6SnS8(H2O)18]8+is obtained by reacting Sn metal with[Mo3S4(H2O)9]4+.The double cube is alsoobtained in ∼50% yield by BH4- reductionof a 1:1 mixture of[Mo3SnS4(H2O)10]6+and[Mo3S4(H2O)9]4+.Conversely two-electron oxidation of[Mo6SnS8(H2O)18]8+with [Co(dipic)2]- or[Fe(H2O6]3+ gives thesinglecube[Mo3SnS4(H2O)12]6+and[Mo3S4(H2O)9]4+(up to 70% yield), followed by further two-electron oxidationto[Mo3S4(H2O)9]4+and SnIV. The kinetics of the first stages have beenstudied using the stopped-flow method andgive rate laws first order in[Mo6SnS8(H2O)18]8+and the CoIII or FeIII oxidant. Theoxidation with[Co(dipic)2]-has no [H+] dependence, [H+] =0.50−2.00 M. With FeIII as oxidant, reaction stepsinvolving [Fe(H2O)6]3+and[Fe(H2O)5OH]2+ areimplicated. At 25 °C and I = 2.00 M (Li(pts))kCo is 14.9 M-1s-1 and ka for thereactionof [Fe(H2O)6]3+ is 0.68M-1 s-1 (bothouter-sphere reactions). Reaction of Cu2+ with thedouble but not thesingle cube is observed, yielding[Mo3CuS4(H2O)10]5+.A redox-controlled mechanism involving intermediateformation of Cu+ and[Mo3S4(H2O)9]4+accounts for the changes observed.
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