Crystal structure of hexakis( N , N -dimethylformamide-κ O )iron(III) μ-chlorido-bis(trichloridocadmium)

The title compound, [Fe(C 3 H 7 NO) 6 ][Cd 2 Cl 7 ], crystallizes in the trigonal space group R \overline{3} and is assembled from discrete [Fe(DMF) 6 ] 3+ cations (DMF = N , N -dimethylformamide) and [Cd 2 Cl 7 ] 3− anions. In the cation, the iron(III) atom, located on a special position of \overline{3} 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 octahedral 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 [Cd 2 Cl 7 ] 3− anion is also located on a special position of \overline{3} site symmetry and bridges two corner sharing, tetrahedrally 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 interactions. There are also C—H...Cl and C—H...O interactions, 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.