Interconversion and Reactivity of Two Heterometallic Tin-Containing Cuboidal Clusters from [Mo(3)S(4)(H(2)O)(9)](4+): X-ray Structure of the Single Cube with an Mo(3)SnS(4) Core

The Mo(3)SnS(4)(6+) single cube is obtained by direct addition of Sn(2+) to Mo(3)S(4)(H(2)O)(9)](4+). UV-vis spectra of the product (0.13 mM) in 2.00 M HClO(4), Hpts, and HCl indicate a marked affinity of the Sn for Cl(-), with formation of the more strongly yellow Mo(3)(SnCl(3))S(4)(H(2)O)(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)(SnCl(3))S(4)(NCS)(9)].0.5H(2)O has been determined and gives Mo-Mo (mean 2.730 ?) and Mo-Sn (mean 3.732 ?) distances, with a difference close to 1 ?. The red-purple double cube cation Mo(6)SnS(8)(H(2)O)(18)](8+) is obtained by reacting Sn metal with Mo(3)S(4)(H(2)O)(9)](4+). The double cube is also obtained in approximately 50% yield by BH(4)(-) reduction of a 1:1 mixture of Mo(3)SnS(4)(H(2)O)(10)](6+) and Mo(3)S(4)(H(2)O)(9)](4+). Conversely two-electron oxidation of Mo(6)SnS(8)(H(2)O)(18)](8+) with Co(dipic)(2)](-) or Fe(H(2)O(6)](3+) gives the single cube Mo(3)SnS(4)(H(2)O)(12)](6+) and Mo(3)S(4)(H(2)O)(9)](4+) (up to 70% yield), followed by further two-electron oxidation to Mo(3)S(4)(H(2)O)(9)](4+) and Sn(IV). The kinetics of the first stages have been studied using the stopped-flow method and give rate laws first order in Mo(6)SnS(8)(H(2)O)(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(H(2)O)(6)](3+) and Fe(H(2)O)(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(H(2)O)(6)](3+) is 0.68 M(-)(1) s(-)(1) (both outer-sphere reactions). Reaction of Cu(2+) with the double but not the single cube is observed, yielding Mo(3)CuS(4)(H(2)O)(10)](5+). A redox-controlled mechanism involving intermediate formation of Cu(+) and Mo(3)S(4)(H(2)O)(9)](4+) accounts for the changes observed.