Iron-gold (or -mercury) carbide clusters derived from [Fe6C(CO)(16)](2-). X-ray crystal structures of (NEt(4))[Fe6C{AuPPh(3)}(CO)(16)] and [Fe4C{AuPPh(3)}(CO)(11)(NO)]

The metal halide complexes ClAuPPh(3) and ClHg(m) react in thf with [Fe6C(CO)(16)](2-) affording the metal cluster compounds (NEt(4))[Fe6C{mu(3)-AuPPh(3)}(CO)(16)] (1) and (NEt(4))[Fe6C{Hg(m)}(CO)(16)] (m = Mo(CO)(3)Cp (2), W(CO)(3)Cp (3), and Mn(CO)(5) (4)) in good yields. The cluster [{Fe6C(CO)(16)}(2)(Hg)](2-) (5) is also isolated by reaction of this anion with Hg(NO3)(2). The product obtained by treatment of 1 with NOBF4 depends on the stoichiometry of the reaction. Thus, with a 1:1 molar ratio the nitrosyl compound [Fe6C(AuPPh(3))(C O)(15)-(NO)] (6) was formed whereas the use of an excess of NOBF4 led to the pentametal cluster [Fe4C{AuPPh(3))(CO)(11)(NO)] (7). The structures of 1 and 7 have been determined by X-ray diffraction methods. The electrochemical behavior of 2-5 has been investigated by cyclic voltammetry and coulometry. An extended Huckel molecular orbital study of the bonding capabilities of [Fe4C{CO)(12)](2-) has been carried out in order to understand the structural differences between [Fe4C{AuPPh(3))(CO)(12)](-) and [HFe4C(CO)(12)](-).