Synthesis and crystal structures of tetraethylammonium μ₃-acetyl-C¹-(Fe¹Fe²)O(Fe ¹Fe³)-nonacarbonyl-triangulo-triferrate and tetraethyl-ammonium μ-carbonyl-nonacarbonyl-μ ₃-2,4-dioxapentylidyne-triangulo-triferrate

The iron carbonylate anion [Fe₂(CO)₈]^2- reacts with iodomethane and with chloromethyl methyl ether to give the tri-iron cluster anions [Fe₃(CO)₉(μ₃-CH₃CO)]^- (1) and [Fe₃(CO)₉(μ-CO)(μ₃-COCH ₂OCH₃)]^- (2) respectively. The structures of the cluster anions have been determined by X-ray diffraction studies of their tetraethylammonium salts. The compound [NEt₄][Fe₃(CO)₉(μ₃-CH ₃CO)] is orthorhombic, space group Pna2₁, with a = 16.559(2), b = 11.986(2), c = 12.142(2) Å, and Z = 4, while [NEt₄][Fe₃(CO)₁₀(μ₃-COCH ₂OCH₃)] is monoclinic, space group P2₁/n, with a = 12.806(2), b = 14.922(2), c = 15.098(2) Å, β = 105.34(2)°, and Z = 4. The structures have been solved and refined by standard procedures to R values of 0.068 and 0.080 respectively using 2 273 and 2 677 observed [I > 1.5σ(I)] diffractometer data. Possible mechanisms for the formation of the anions are considered.