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

Abstract 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 ] ∞ , 1 , and extended three-dimensional structure of [{Na(DMF) 1.25 } 2 Fe(CO) 4 ] ∞ , 2 . The existence of such an interaction is supported by observed short K–Fe and Na–Fe distances of 3.594(1) A and 2.899(1) A and short K–C and Na–C distances of 3.080(3) A and 2.792(4) A. 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 ]·1.5(C 4 H 8 O 2 ) 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 [PPh 4 ] + salts. The structure of the [Ru 2 (CO) 8 ] 2− anion differs from that previously reported for [PPh 4 ][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.