Synthesis and Chemical and Electrochemical Characterization of Fe-S Carbonyl Clusters. X-ray Crystal Structures of [N(PPh(3))(2)](2)[Fe(5)S(2)(CO)(14)] and [N(PPh(3))(2)](2)[Fe(6)S(6)(CO)(12)].

A reinvestigation of the redox behavior of the Fe(3)(&mgr;(3)-S)(CO)(9)(-) dianion led to the isolation and characterization of the new Fe(5)S(2)(CO)(14)(-), as well as the known Fe(6)S(6)(CO)(12)(-) dianion. As a corollary, new syntheses of the Fe(3)S(CO)(9)(-) dianion are also reported. The Fe(5)S(2)(CO)(14)(-) dianion has been obtained by oxidative condensation of Fe(3)S(CO)(9)(-) induced by tropylium and Ag(I) salts or SCl(2), or more straightforwardly through the reaction of Fe(4)(CO)(13)(-) with SCl(2). The Fe(6)S(6)(CO)(12)(-) dianion has been isolated as a byproduct of the synthesis of Fe(3)S(CO)(9)(-) and Fe(5)S(2)(CO)(14)(-) or by reaction of Fe(4)(CO)(13)(-) with elemental sulfur. The structures of N(PPh(3))(2)[Fe(5)S(2)(CO)(14)] and N(PPh(3))(2)[Fe(6)S(6)(CO)(12)] were determined by single-crystal X-ray diffraction analyses. Crystal data: for N(PPh(3))(2)[Fe(5)S(2)(CO)(14)], monoclinic, space group P2(1)/c (No. 14), a = 24.060(5), b = 14.355(6), c = 23.898(13) Å, beta = 90.42(3) degrees, Z = 4; for N(PPh(3))(2)[Fe(6)S(6)(CO)(12)], monoclinic, space group C2/c (No. 15), a = 34.424(4), b = 14.081(2), c = 19.674(2) Å, beta = 115.72(1) degrees, Z = 4. The new Fe(5)S(2)(CO)(14)(-) dianion shows a "bow tie" arrangement of the five metal atoms. The two Fe(3) triangles sharing the central Fe atom are not coplanar and show a dihedral angle of 55.08(3) degrees. Each Fe(3) moiety is capped by a triply bridging sulfide ligand. The 14 carbonyl groups are all terminal; two are bonded to the unique central atom and three to each peripheral iron atom. Protonation of the Fe(5)S(2)(CO)(14)(-) dianion gives reversibly rise to the corresponding HFe(5)S(2)(CO)(14) monohydride derivative, which shows an (1)H-NMR signal at delta -21.7 ppm. Its further protonation results in decomposition to mixtures of Fe(2)S(2)(CO)(6) and Fe(3)S(2)(CO)(9), rather than formation of the expected H(2)Fe(5)S(2)(CO)(14) dihydride. Exhaustive reduction of Fe(5)S(2)(CO)(14)(-) with sodium diphenyl ketyl progressively leads to fragmentation into Fe(3)S(CO)(9)(-) and Fe(CO)(4)(-), whereas electrochemical, as well as chemical oxidation with silver or tropylium tetrafluoroborate, in dichloromethane, generates the corresponding Fe(5)S(2)(CO)(14) radical anion which exhibits an ESR signal at g = 2.067 at 200 K. The electrochemical studies also indicated the existence of a subsequent one-electron anodic oxidation which possesses features of chemical reversibility in dichloromethane but not in acetonitrile solution. A reexamination of the electrochemical behavior of the Fe(3)S(CO)(9)(-) dianion coupled with ESR monitoring enabled the spectroscopic characterization of the Fe(3)S(CO)(9) radical monoanion and demonstrated its direct involvement in the generation of the Fe(5)S(2)(CO)(14)()(-) (n = 0, 1, 2) system.