Electrochemical, spectroscopic, structural, and magnetic characterization of the reduced and protonated α-Dawson anions in [Fe(η5-C5Me5)2]5[HS2Mo18O62]•3HCONMe2•2Et2O and [NBu4]5[HS2Mo18O62]•2H2O1

Reaction of excess Fe(CP*)(2) (cp(*) = n(5)-C5Me5) dissolved in Et2O with [NHex(4)](4)[S2Mo18O62] in acetonitrile, followed by recrystallization of the precipitated solid from N,N-r-dimethylformamide (DMF), leads to isolation of the complex [Fe(cp(*))(2)](5)[HS2Mo18O62].3DMF.2Et(2)O. The solid has been characterized by microanalysis, by voltammetric analysis, by H-1 NMR, diffuse reflectance infrared, EPR, and Mossbauer spectroscopies, and by temperature-dependent magnetic susceptibility measurements. The data are consistent with the presence of a paramagnetic [Fe(cp(*))(2)](+) cation and a diamagnetic two-electron-reduced [HS2Mo18O62](5-) anion. The related salt [NBu4](5)[HS2Mo18O62].2H(2)O crystallizes in space group C2/c with a = 25.1255(3) (A) over circle, b = 15.4110(2) (A) over circle, c = 35.8646(4) (A) over circle, beta = 105.9381(4)degrees, V = 13353,3(3) (A) over circle (3), and Z = 4. The (2 e(-), 1 H+)-reduced anion exists as the alpha-Dawson isomer, and its structure may be compared with those of the oxidized and (4 e(-), 3 H+)-reduced anions as they exist in [NEt4](4)[S2Mo18O62].MeCN and [NBu4](5)[H3S2Mo18O62].4MeCN, respectively. Overall, the anion expands significantly upon the addition of two and then four electrons. However, the Mo...Mo distances along the bonds which connect the two equatorial belts decrease in the order 3.801, 3.780, and 3.736 (A) over circle, making these distances the shortest for the three inequivalent sets of corner-sharing octahedra in each anion. This is consistent with the two or four added electrons localizing essentially in molecular orbitals which are bondiing with respect to interactions between the belts.