Inorganic Chemistry, Vol.41, No.25, 6726-6730, 2002
Synthesis and structures of one- and two-electron oxidized forms of bis(acetylene)tetrairon clusters Cp' Fe-4(4)(HCCH)(2) (Cp'=Cp, eta(5)-C5H4Me)
Air-oxidation of Cp'Fe-4(4)(HCCH)(2) (Cp' = Cp (1a), C5H4Me (1b)) in an NH4PF6/CH3CN solution afforded the one-electron oxidized clusters [Cp'Fe-4(4)(HCCH)(2)](PF6). Oxidation of 1a with excess AgBF4 in THF afforded [1a](BF4), while that of 1b with excess AgBF4 gave [1b](BF4)(2). The X-ray crystal structure analysis of [1a](BF4) revealed that the monocationic cluster retains the butterfly-type Fe-4(mu(4)-eta(2):eta(2):eta(1):eta(1)-HCCH)(2) framework similar to that of the neutral cluster. The average Fe-Fe bond length is shorter by 0.029 Angstrom than that in the neutral cluster. Electrochemical oxidation of 1a and 1b in 0.1 M NH4PF6/CH3CN solution at +0.30 and +0.25 V versus Ag/10 mM AgNO3, respectively, afforded the two-electron oxidized clusters [1a](PF6)(2) and [1b](PF6)(2). The X-ray crystal structure analysis for [1b]-(BF4)(2) shows that the butterfly-type cluster core is retained but shrinks more of those of neutral and monocationic clusters. The four Fe-Fe bonds in [1b](BF4)(2) are unequivalent: one Fe-Fe bond (2,397(1) Angstrom) is apparently shorter than the others (2.439(2)-2.461(2) Angstrom).