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)}(2)Fe(CO)(4)](infinity), 1, and extended three-dimensional structure of [{Na(DMF)(1.25)}(2)Fe(CO)(4)](infinity), 2. The existence of such an interaction is supported by observed short K-Fe and Na-Fe distances of 3.594(1) angstrom and 2.899(1) angstrom and short K-C and Na-C distances of 3.080(3) angstrom and 2.792(4) angstrom. 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 Na-2[Fe(CO)(4)]center dot 1.5(C4H8O2) and K-2[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)[M-2(CO)(8)] (M = Fe, 3; Ru, 4) are isomorphous. They are ion pair complexes in which the [M-2(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 [Fe-2(CO)(8)](2-) anion is similar to that in the [PPN](+) and [PPh4](+) salts. The structure of the [Ru-2(CO)(8)](2-) anion differs from that previously reported for [PPh4][Ru-2(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. (C) 2012 Elsevier B. V. All rights reserved.