Formal reduction potentials (E°' values vs. Ag/Ag+ given in parentheses) in acetonitrile of 1-ferrocenyl-4,4,4-trifluorobutane-1,3-dione (ferrocenoyltrifluoroacetone, Hfctfa, 0.394 V), 1-ferrocenyl-4,4,4-trichlorobutane-1,3-dione (ferrocenoyltrichloroacetone, Hfctca, 0.370 V), 1-ferrocenylbutane-1,3-dione (ferrocenoylacetone, Hfca, 0.313 V), 1-ferrocenyl-3-phenylpropane-1,3-dione (benzoylferrocenoylmethane, Hbfcm, 0.306 V), and 1,3-diferrocenylpropane-1,3-dione (diferrocenoylmethane, Hdfcm, 0.265 and 0.374 V for the two electrochemically nonequivalent ferrocenyl groups) were determined. A linear relationship between observed group electronegativity, χ, and E°' as well as observed infrared carbonyl stretching frequencies of methyl esters of the type RCOOMe resulted in average χ-values, on the Gordy scale, of 1.87 for the ferrocenyl group and 2.82 for the ferrocenium group. A single crystal X-ray structure determination of Hfctfa (monoclinic, P21/n, Z = 4, R = 0.029) showed that this β-diketone crystallizes in the enol form. Asymmetric enolization in a direction furthest from the aromatic ferrocenyl group was observed.Key words: ferrocene, β-diketone, group electronegativity, cyclic voltammetry.

The complex [Mo,S4(OH,),IQ+ possesses non-equivalent H, O ligands with those (d, two per Mo) which are trans to p-S undergoing water exchange 1 O5 faster than those (c, one per M o ) which are trans to p3-S.The former arises from a labilising pathway involving the monohydroxo conjugate base [Mo& (OH2),(OH)I3'

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.

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