Structures of DMF solvated potassium and sodium salts of [Fe(CO)4]2− and [M2(CO)8]2− (M = Fe, Ru)

An electrostatic interaction was detected between an alkali metal cation and the [Fe(CO)4]2− anion in the extended two-dimensional structure of [{K(DMF)}2Fe(CO)4]∞, 1, and extended three-dimensional structure of [{Na(DMF)1.25}2Fe(CO)4]∞, 2. The existence of such an interaction is supported by observed short K–Fe and Na–Fe distances of 3.594(1) Å and 2.899(1) Å and short K–C and Na–C distances of 3.080(3) Å and 2.792(4) Å. In addition to the electrostatic interactions, typical isocarbonyl linkages were also existed between the alkali metal cation and the [Fe(CO)4]2− anion. These two interactions lead to the extended multi-dimensional structures of 1 and 2. The [Fe(CO)4]2− anion basically retains tetrahedral geometry in 1 and 2, different from that in the complexes Na2[Fe(CO)4]·1.5(C4H8O2) and K2[Fe(CO)4] in which the [Fe(CO)4]2− anion is significantly distorted from a tetrahedral arrangement. The structures of [Na(DMF)3]2[M2(CO)8] (M = Fe, 3; Ru, 4) are isomorphous. They are ion pair complexes in which the [M2(CO)8]2− anions consist of two trigonal bipyramidal M(CO)4 fragments joined at axial sites. The cations have trigonal antiprismatic coordination geometry. The structure of the [Fe2(CO)8]2− anion is similar to that in the [PPN]+ and [PPh4]+ salts. The structure of the [Ru2(CO)8]2− anion differs from that previously reported for [PPh4][Ru2(CO)8]. In that case the dianion consists of a trigonal–bipyramidal Ru(CO)4 fragment joined to a basal site of a four-sided pyramidal Ru(CO)4 fragment.