Crystal structure of tetrakis(acetylacetonato)dichloridodi-μ3-methanolato-tetra-μ2-methanolato-tetrairon(III)

The molecular structure of [Fe4Cl2(acac)4(OMe)6] (acac = acetylacetonate) consists of a face-sharing double cubane cluster with two opposite corners missing. Weak C—H⋯Cl intermolecular interactions result in a two-dimensional extended sheet structure normal to the b axis.

We have investigated the syntheses of metal methoxysilanolates via the additions of NaOSi(OMe) 2 Me to metal ISSN 2056-9890 halides and discovered that, in certain cases, the addition of NaOSi(OMe) 2 Me to a metal halide results in the formation of a methanolate complex instead of silanolate complex. In line with this observation, we now report that the addition of NaOSi(OMe) 2 Me to Fe(acac) 2 Cl results in the formation of a tetranuclear iron(III) methanolate compound, Fe 4 (acac) 4 ( 2 -OMe) 4 ( 3 -OMe) 2 Cl 2 , (I).

Structural commentary
The structure of (I) contains two crystallographically independent Fe III metal atoms. Both cations are in approximately octahedral coordination environments. The coordination sphere of Fe1 is filled by the O atoms of one 2 -acac ligand [Fe1-O1 = 1.9971 (13) Å and Fe1-O2 = 1.9934 (13)  The molecular structure of (I) (Fig. 1) can be described as an [Fe 4 (OMe) 6 ] face-sharing double pseudo-cubane entity with two opposite corners missing. The outside of the cluster is decorated by one acac ligand per metal and the Fe atoms at either end of the cluster are coordinated by one chloride ion. Neighboring FeÁ Á ÁFe distances range from 3.1997 (4) to 3.2175 (6) Å , while the Fe1Á Á ÁFe1 i distance is 5.5702 (6) Å .

Supramolecular features
There are no significant supramolecular features to discuss with the extended structure of (I). There are weak interactions View of the molecular structure of (I), showing the atomic numbering and 35% probability displacement ellipsoids for the non-H atoms. The unlabeled atoms are related to the labeled ones by the symmetry operator (Àx + 1, Ày + 1, Àz + 1). H atoms have been removed for clarity.

Figure 2
A view along the b axis of the extended two-dimensional network of (I) with an overlay of the unit cell. The intermolecular Cl-H interations are shown as dashed red lines. All C atoms except those in the hydrogenbonded acac ligand and all H atoms except those of the hydrogen-bonded methyl group have been removed for clarity. Color key: blue = Fe, lightgreen = Cl, red = O, gray = C, and green = H.

Table 1
Hydrogen-bond geometry (Å , ). between the Cl À ion and an acac ligand on neighboring molecules (Table 1). Taking into account these weak interactions, the extended structure becomes layers of two-dimensional 4 4nets normal to the b axis (Fig. 2).

Database survey
One closely related complex, [Fe 4 (acac) 4 (OMe) 6 (N 3 ) 2 ], has previously been reported (Li et al., 1997) in which N 3 À takes the position of Cl À in (I). The molecular structure of the azide complex is very similar to that of (I), and can be described as the same [Fe 4 (OMe) 6 ] face-sharing double cubane cluster with two opposite corners missing. The average Fe-O acac distance of 1.978 Å is quite close to the average Fe-O acac distance of 1.982 Å in (I). The average Fe-OMe distances in the azide complex ( 2 -OMe: 1.977 Å ; 3 -OMe: 2.124 Å ) are also comparable to those in (I) ( 2 -OMe: 1.983 Å ; 3 -OMe: 2.125 Å ).
A search of the Cambridge Structural Database (Groom & Allen, 2014) returned 14 complexes with an [Fe 4 (OR) 6 ] cluster core similar to (I) (Abu-Nawwas et al., 2009;Mulyana et al., 2009). All of these materials, except the azide compound described above, use more complex, multidentate ligands to form the polynuclear entity. The [Fe 4 (OR) 6 ] motif is present is 63 additional materials as part of a higher-order cluster complex (Ferguson et al., 2013;Murugesu et al., 2004).

Synthesis and crystallization
A solution of NaOSi(OMe) 2 Me (57 mg, 3.96 Â 10 À4 mol, 1 equivalent) in THF (3 ml) was added to a solution of Fe(acac) 2 Cl (200 mg, 3.96 Â 10 À4 mol, 1 equivalent) in THF (see Scheme). The mixture was stirred rapidly at room temperature, and a slight color change from a dark-red to a lighter red was observed. Removal of the solvent under vacuum resulted in the precipitation of an orange solid, which upon washing with dry Et 2 O (2 Â 10 ml) left a yellow solid. The yellow solid was extracted into dry CH 2 Cl 2 and filtered through Celite. The CH 2 Cl 2 was then removed under vacuum, leaving a yellow solid (54 mg, 6.16 Â 10 À5 mol, 62% yield). Crystals suitable for X-ray diffraction were grown by slow diffusion of pentane into a CH 2 Cl 2 solution of the yellow solid.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Methyl-H atom positions, RCH 3 , were optimized by rotation about R-C bonds, with idealized C-H, R-H and HÁ Á ÁH distances (C-H = 0.98 Å ). The remaining H atoms were included as riding idealized contributors (C-H = 0.95 Å ). H atoms were assigned U iso (H) = 1.5U eq (C) for methyl H atoms and U iso (H) = 1.2U eq (C) otherwise. The 102 reflection was omitted from the final refinement because it was partially obscured by the shadow of the beam stop.

Special details
Experimental. One distinct cell was identified using APEX2 (Bruker, 2013). Four frame series were integrated and filtered for statistical outliers using SAINT (Bruker, 2013) then corrected for absorption by integration using SADABS v2012/1 (Bruker, 2012). No decay correction was applied. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Structure was phased by intrinsic phasing methods (XT, Sheldrick, 2013). Systematic conditions suggested the unambiguous space group. The space group choice was confirmed by successful convergence of the full-matrix leastsquares refinement on F 2 . The final difference Fourier had no significant features. A final analysis of variance between observed and calculated structure factors showed little dependence on amplitude or resolution.