Interconversion and reactivity of two heterometallic tin-containing cuboidal clusters from [Mo3S4(H2O)(9)](4+): X-ray structure of the single cube with an Mo3SnS4 core

The Mo3SnS46+ single cube is obtained by direct addition of Sn2+ to [Mo3S4(H2O)(9)](4+). UV-vis spectra of the product (0.13 mM) in 2.00 M HClO4, Hpts, and HCl indicate a marked affinity of the Sn for Cl-, with formation of the more strongly yellow [Mo-3(SnCl3)S-4(H2O)(9)](3+) complex complete in as little as 0.050 M Cl-. The X-ray crystal structure of (Me(2)NH(2))(6)[Mo-3(SnCl3)S-4(NCS)(9)]. 0.5H(2)O has been determined and gives Mo-Mo (mean 2.730 Angstrom) and Mo-Sn (mean 3.732 Angstrom) distances, with a difference close to 1 Angstrom. The red-purple double cube cation [Mo6SnS8(H2O)(18)](8+) is obtained by reacting Sn metal with [Mo3S4(H(2)0)(9)](4+). The double cube is also obtained in similar to 50% yield by BH4- reduction of 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 the single cube [Mo3SnS4(H2O)(12)](6+) and [Mo3S4(H2O)(9)](4+) (up to 70% yield), followed by further two-electron oxidation to [Mo3S4(H2O)(9)](4+) and Sn-IV. The kinetics of the first stages have been (s)tudied using the stopped-flow method and give rate laws first order in [Mo6SnS8(H2O)(18)](8+) and the Co-III or Fe-III oxidant. The oxidation with [Co(dipic)(2)](-) has no [H+] dependence, [H+] = 0.50-2.00 M. With Fe-III as oxidant, reaction steps involving [Fe(H2O)(6)](3+) and [Fe(H2O)(5)OH](2+) are implicated. At 25 degrees C and I = 2.00 M (Li(pts)) k(Co), is 14.9 M(-1)s(-1) and k(a) for the reaction of [Fe(H2O)(6)](3+) is 0.68 M(-1) s(-1) (both outer-sphere reactions). Reaction of Cu2+ With the double but not the single cube is observed, yielding [Mo3CuS4(H2O)(10)]5(+). A redox-controlled mechanism involving intermediate formation of Cu+ and [Mo3S4(H2O)(9)](4+) accounts for the changes observed.