Dicarbonyldichloridobis(trimethylphosphane)iron(II)–carbonyldichloridotris(trimethylphosphane)iron(II)–tetrahydrofuran (1/1/2)

The asymmetric unit of the title crystal, [FeCl2(C3H9P)3(CO)]·[FeCl2(C3H9P)2(CO)2]·2C4H8O, contains half molecules of the two closely related FeII complexes lying on mirror planes and a tetrahydrofuran solvent molecule, one C atom of which is disordered over two sets of sites with site occupancy factors 0.633 (9) and 0.367 (9). In both FeII complex molecules, a distorted octahedral coordination geometry has been observed around the Fe atoms. Weak intermolecular C—H⋯O interactions are observed in the crystal structure.

The asymmetric unit of the title crystal, [FeCl 2 (C 3 H 9 P) 3 -(CO)]Á[FeCl 2 (C 3 H 9 P) 2 (CO) 2 ]Á2C 4 H 8 O, contains half molecules of the two closely related Fe II complexes lying on mirror planes and a tetrahydrofuran solvent molecule, one C atom of which is disordered over two sets of sites with site occupancy factors 0.633 (9) and 0.367 (9). In both Fe II complex molecules, a distorted octahedral coordination geometry has been observed around the Fe atoms. Weak intermolecular C-HÁ Á ÁO interactions are observed in the crystal structure.

Related literature
For the synthetic background, see: Harris et al. (1978). For the crystal structure of a related complex, see: Venturi et al.  Table 1 Hydrogen-bond geometry (Å , ). been cocrystallized along with a molecule of tetrahydrofuran solvate per molecule of complex (Fig. 1).
The asymmetric unit of the title crystal contains half molecules of the two compounds, (I) and (II), lying on mirror planes and a molecule of tetrahydrofuran solvate, C 4 H 8 O; a carbon atom of the solvent molecule is disordered over two sites C4S and C4S' with site occupancy factors 0.633 (9) and 0.367 (9). In compound (I), the PMe 3 ligands occupying axial positions, are trans with respect to each other with an angle of 175.20 (4)° and the CO and Cl are trans with respect to each other at equatorial positions. In compound (II), the trans PMe 3 ligands are located at 166.41 (4)° to each other; the 3 rd PMe 3 is trans to a Cl. The octahedral coordination is completed with the 2nd Cl being trans to a CO ligand. In both compounds, the ligands around Fe lie in slightly distorted octahedral coordination geometry. An overlay plot of the two molecules drawn by Mercury (Macrae et al., 2008) shows the close similarity of the two molecules (Fig. 2).
There are weak intermolecular interactions of the type C-H···O which are observed between both the carbonyl O atoms of (I) and a methyl hydrogen atom of (II). The O of the solvent THF also has weak interactions with a methyl hydrogen atoms of (II) ( Table 1).

Experimental
FeCl 2 (0.21 g, 1.62 x 10 -3 mol) and PMe 3 (0.40 ml, 3.86 x 10 -3 ) were stirred in 20 ml of THF for 10 min, producing a clear gray solution of Cl 2 Fe(PMe 3 ) 2 (Harris et al., 1978) in the presence of excess PMe 3 . Carbon monoxide was then bubbled through the solution until the color changed to an intense orange. The THF solvent was removed under vacuum and the resulting powder was extracted with pentane. After filtration through Celite, the pentane was removed under vacuum. The product was dissolved in a 1:2 mixture of THF and pentane and cooled to 243 K, causing orange crystals to form overnight.

Refinement
H atoms bonded to the C atoms located on the mirror planes were located in a difference map and refined using a riding model. Other H atoms were calculated with idealized geometries with C-H = 0.98 and 0.99 Å for methyl and methylene type H-atoms, respectively, and refined using a riding model with U iso (H) = 1.2 (1.5 for methyl groups) times U eq (C). A molecule of THF was located in the asymmetric unit wherein C4 was disordered with partial occupancy factors 0.633 (9) and 0.367 (9). supplementary materials sup-2 Figures Fig. 1. The molecular structure of (I) and (II) with atom labels and 50% probability displacement ellipsoids for non-H atoms. Disordered atoms in the solvent are omitted for clarity. Symmetry codes represented by A in atomic labels: for (I) = x, 0.5 -y, z and for (II) = x, 1.5 -y, z.