Transition Metal Triangles and Clusters

Flash photolysis of the dianion of Roussin s Red Salt, [Fe2S2(NO)4]2, in particular the initial photoinitiated loss of NO (382) and the reverse recombination reaction, en route to the eventual product, the anion of Roussin s Black Salt, [Fe4S3(NO)7] , has been documented (383). A 4-RC6H4S group (R = H, Me, OMe, Cl, or CF3) replaces one of the chloride ligands in [Fe4S4Cl4]2 via a five-coordinated intermediate, with the detailed sequence of steps acid-dependent (384). Loss of chloride is 

The dependence of rate constants for approach to equilibrium for reaction of the mixed oxide-sulfide complex [Mo3((i3-S)((i-0)3(H20)9] 1+ with thiocyanate has been analyzed into formation and aquation contributions. These reactions involve positions trans to p-oxo groups, mechanisms are dissociative (391). Kinetic and thermodynamic studies on reaction of [Mo3MS4(H20)io]4+ (M = Ni, Pd) with CO have yielded rate constants for reaction with CO. These were put into context with substitution by halide and thiocyanate for the nickel-containing cluster (392). A review of the chemistry of [Mo3S4(H20)9]4+ and related clusters contains some information on substitution in mixed metal derivatives [Mo3MS4(H20)re]4+ (M = Cr, Fe, Ni, Cu, Pd) (393). There are a few asides of mechanistic relevance in a review of synthetic Mo-Fe-S clusters and their relevance to nitrogenase (394). 

The mechanism of formation of corner-shared double cubes [Mo6HgE8 (H20)18]8+ (E = S, Se) involves reaction of [Mo3E4(H20)9]4+ with Hg° or Hg2+.The first-order dependence on [Mo3E4(H20)9]4+ suggests that the mechanism involves reaction of [Mo3E4]4+ with Hg, followed by reaction with the second [Mo3E4]4+ unit, rather than reaction of two [Mo3E4]4+ units followed by incorporation of the mercury (395). 

The clusters [Re6Se8(PEt3)5(MeCN)]2+ and [Re6Se8(PEt3)5(dmso)]2+ are substitutionally inert, with MeCN and dmso exchange or 

Two hexanuclear zinc clusters are mentioned elsewhere in this Chapter, one in Section V.A.7 (on zinc(II) reactions) above, the other in Section VII.D (on supramolecular chemistry) below. 

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VI. Transition Metal Triangles and Clusters VII. Reactions of Coordinated Ligands... 

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