Synthesis and characterization of pentanuclear Fe–Ir carbonyl clusters. Solid-state structures of [N(PPh3)2]2[FeIr4(CO)15] and [PPh4][Fe2Ir3(CO)14]

Abstract

The dianion [FeIr₄(CO)₁₅]^2– can be obtained by reduction of an equimolar mixture of [Fe(CO)₅] and [Ir₄(CO)₁₂] in alcoholic NaOH and under 1 atm of carbon monoxide. The salt [N(PPh₃)₂]₂[FeIr₄(CO)₁₅](1) crystallizes in the triclinic space group P with unit-cell dimensions a= 11.399(3), b= 14.032(3), c= 29.163(4)Å, α= 86.18(2), β= 84.52(2), γ= 80.14(2)°, and Z= 2. Its metal framework consists of a trigonal bipyramid with the equatorial triangle formed by iridium atoms. The mean values of the Fe–Ir, Ir_eq–Ir_eq′ and Ir_ap–Ir_eq distances are 2.943, 2.708, 2.991 Å, respectively. The monoanion [Fe₂Ir₃(CO)₁₄]^– was obtained from [Fe(CO)₄]^2– and [Ir(CO)₂Cl₂]^–. The salt [PPh₄][Fe₂Ir₃(CO)₁₄](2) crystallizes in the orthorthombic space group P2₁2₁2₁ with unit-cell dimensions a= 12.461(5), b= 14.306(5), c= 23.504(6)Å, and Z= 4. Its metallic framework is comprised of an iridium triangle capped on opposite side by two iron atoms. The mean values of the Fe–Ir and Ir–Ir distances are 2.648 and 2.708 Å, respectively. In the derivative (1) the trigonal bipyramid is considerably elongated in the direction of the apical atoms, When compared with that in (2). This elongation is consistent with the increased number of cluster valence electrons: 76 in (1) and 72 in (2).