Preparation and Solution Properties of Chalcogenide-Rich Clusters [Mo(3)Y(7)(H(2)O)(6)](4+) (Y = S, Se): Kinetics of PR(3)(3-) Abstraction of Y from &mgr;-(Y(2)(2-)) and H(2)O Substitution by Cl(-) and Br(-).

The chalcogenide-rich trinuclear Mo(IV)(3) clusters [Mo(3)Y(7)(H(2)O)(6)](4+), containing single &mgr;(3)-(Y(2)(-)) and three &mgr;-(Y(2)(2)(-)) core ligands, have been obtained for the first time from polymeric {Mo(3)Y(7)Br(4)}(x)() via [Mo(3)Y(7)Br(6)](2)(-) (Y = S, Se). ICP analyses of 2 M HCl solutions give Mo:S and Mo:Se ratios consistent with the formulas indicated, and on reaction with concentrated HBr, 85% recovery of (Et(4)N)(2)[Mo(3)S(7)Br(6)], the structure of which is known, has been achieved. Abstraction of S and Se with PPh(3) (two-phase system), or the water-soluble phosphine (3-SO(3)C(6)H(4))(3)P(3)(-) (PR(3)(3)(-)), gives quantitative formation of [Mo(3)S(4)(H(2)O)(9)](4+) and [Mo(3)Se(4)(H(2)O)(9)](4+). With CN(-), both abstraction of S (or Se) and CN(-) replacement of H(2)O is observed, giving [Mo(3)S(4)(CN)(9)](5)(-) and [Mo(3)Se(4)(CN)(9)](5)(-) as products. It was possible to assign which atom of the sideways eta(2),eta(2) &mgr;-(S(2)(2)(-)) and &mgr;-(Se(2)(2)(-)) ligands is abstracted using the structurally characterized [Mo(3)S(4)Se(3)(H(2)O)(6)](4+) cluster. Thus it was demonstrated that with the phosphines the equatorial (to the Mo(3) plane) Se atoms of the three &mgr;-(SSe(2)(-)) groups are removed with formation of the Mo(3)S(4)(4+) core. Kinetic studies on the reactions of [Mo(3)S(7)(H(2)O)(6)](4+) and [Mo(3)Se(7)(H(2)O)(6)](4+) with PR(3)(3)(-) give approximately 10(3) faster abstraction rate constants (k(a)/M(-)(1) s(-)(1)) for S than Se. The rate law k(a) = k(1)[H(+)] + k(-)(1)[H(+)](-)(1) is explained by the involvement of protonated &mgr;-(Y(2)(2)(-)) (k(1)) and an H(2)O conjugate-base form (k(-)(1)). Equilibration rate constants for X(-) = Cl(-) and Br(-) substitution of H(2)O on [Mo(3)S(7)(H(2)O)(6)](4+) and [Mo(3)Se(7)(H(2)O)(6)](4+) are however independent of [H(+)] in the range 0.5-2.0 M investigated. With X(-) concentrations up to 1.3 M (S cluster) and 0.3 M (Se), the uniphasic reactions are assigned as substitution of the H(2)O cis to &mgr;(3)-(Y(2)(-)) at each Mo. At 25 degrees C formation rate constants 10(4)k(f)/M(-)(1) s(-)(1) are as follows for [Mo(3)S(7)(H(2)O)(6)](4+): Cl(-) (1.83); Br(-) (2.07). The same rate constants are as follows for [Mo(3)Se(7)(H(2)O)(6)](4+): Cl(-) (6.7); Br(-) (33). Formation rate constants for Cl(-) are surprisingly 2 x 10(6) times slower than for the reaction of [Mo(3)S(4)(H(2)O)(9)](4+) with Cl(-). Reactions of Mo(3)S(7)(4+) with three metals (Sn, Ni, In) were studied briefly.

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 Å) and Mo-Sn (mean 3.732 Å) distances, with a difference close to 1 Å. 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.

Aqueous Solution Chemistry of the Mo(3)PdS(4) Cube: Substitution Reactions and the Double to Single Cube Interconversion Induced by CO, Two Phosphines, Cl(-), Br(-), and NCS(-).

The kinetics of conversion of an edge-linked double cube, in this case [{Mo(3)PdS(4)(H(2)O)(9)}(2)](8+), to the corresponding single cube [Mo(3)(PdX)S(4)(H(2)O)(9)](4+), has been studied for the first time. Reaction is induced by six reagents X = CO, two water-soluble phosphines, Cl(-), Br(-), and NCS(-), which complex at the tetrahedral Pd. The first stage of reaction is fast and is accompanied by color changes, e.g. purple to dark blue in the case of Cl(-), assigned as double to single cube conversion. With X = CO and the two phosphines, when absorbance changes are intense enough for stopped-flow monitoring with reactants at Pd-SCN. On removal of e.g. Cl(-) by chromatography or addition of Ag(+), the double cube re-forms.