Crystal structure of hexa-kis-(N, N-di-methyl-form-amide-κ O)iron(III) μ-chlorido-bis-(tri-chlorido-cadmium)

Abstract

The title compound, [Fe(C₃H₇NO)₆][Cd₂Cl₇], crystallizes in the trigonal space group R and is assembled from discrete [Fe(DMF)₆]³⁺ cations (DMF = N,N-di-methyl-formamide) and [Cd₂Cl₇]^3- anions. In the cation, the iron(III) atom, located on a special position of site symmetry, is coordinated by six oxygen atoms from DMF ligands with all Fe-O distances being equal [2.0072 (16) Å]. A slight distortion of the octa-hedral environment of the metal comes from the cis O-Fe-O angles deviating from the ideal value of 90° [86.85 (7) and 93.16 (7)°] whilst all the trans angles are strictly 180°. The central Cl atom of the [Cd₂Cl₇]^3- anion is also located on a special position of site symmetry and bridges two corner sharing, tetra-hedrally coordinated Cd^II atoms. The two Cd atoms and the central Cl atom are colinear. The two sets of terminal chloride ligands on either side of the dumbbell-like anion are rotated relative to each other by 30°. In the crystal, the cations and anions, stacked one above the other along the c-axis direction, are held in place principally by electrostatic inter-actions. There are also C-H⋯Cl and C-H⋯O inter-actions, but these are rather weak. Of the six crystal structures reported to date for ionic salts of [Fe(DMF)₆] ⁿ⁺ cations (n = 2, 3), five contain Fe^II ions. The title compound is the second example of a stable compound containing the [Fe(DMF)₆]³⁺ cation. The existence of both [Fe(DMF)₆]²⁺ and [Fe(DMF)₆]³⁺ cations shows that the DMF ligand coordination sphere can accommodate changes in the charge and spin states of the metal centre.

Keywords: FeIII; N,N-di­methyl­formamide; crystal structure; ionic salt; polychloride dicadmium anion.