Crystal structure of 1-phenylimido-1-{6-[1-(phenylimino)ethyl]pyridin-2-yl}ethan-1-yl-κ3 N,N′,N′′)iron(II)

In the structure of the iron(II) title compound with tridentate radical anionic 2,6-bis[1-(phenylimino)ethyl]pyridine ligands, two independent half-molecules are present in the asymmetric unit.

An analogue of 1 containing a para-methoxy substituent on the imine-phenyl ring, {2,6-(4-MeO-C 6 H 4 -N CMe) 2 -C 5 H 3 N} 2 Fe (2) was also crystallized with two independent molecules in the asymmetric unit (Wile et al., 2009), and it is interesting to compare the geometric parameters of 1 and 2. As observed for 1, the N(imine)-Fe bond lengths in one of the two independent molecules in the asymmetric unit of 2 are similar [2.1278 (19) Bis(imino)pyridine ligands are redox-active owing to the extensive -conjugation (de Bruin et al., 2000;Budzelaar et al., 2001;Knijnenburg et al., 2006). Reduction of the ligand causes characteristic changes in bond lengths, as expected from the resonance structures of the mono-reduced ligand as shown in Fig. 3 (Bart et al., 2006). In particular, reduction by 1 e À lengthens the C(imine)-N(imine) bond length from ca 1.28 to 1.32 Å and shortens the C(imine)-C(ipso) bond length from ca 1.50 to 1.44 Å . In the free ligand, the C(imine)-N(imine) and C(imine)-C(ipso) bond lengths are 1.266 (4) and 1.497 (5) Å (Mentes et al., 2001). The electronic structure of 2 was shown to consist of an Fe II atom and two mono-reduced bis(imino)pyridine radical anions by Mö ssbauer spectroscopy, magnetic data, crystallographic data and broken-symmetry

Supramolecular features
The structure crystallizes in the orthorhombic Ccce space group (No. 68) with rather large unit-cell parameters (b and c axes are both greater than 30 Å ). Fig. 4 shows the crystal packing with Fe atoms forming a sub-lattice with ' 1/4 of the cell volume. The different relative orientation of ligands around the central Fe atoms leads to the obtained large unit cell. In the crystal, the Fe-containing complexes are not involved in any particular direct intermolecular interactions. The shortest CÁ Á ÁH Ar contacts with neighboring phenyl groups start at about 3.2 Å . Orthogonal views of the crystal packing of 1 projected along the a (left) and c (right) axes. Fe atoms are shown as large brown spheres of arbitrary radius.

Figure 3
Resonance structures of the mono-reduced ligand in 1.

Synthesis and crystallization
Compound 1 was isolated from the attempted synthesis of (PDI)FeCl by reduction of (PDI)FeCl 2 with NaHBEt 3 in Et 2 O. Et 2 O (10 ml) was added to (PDI)FeCl 2 (0.113 g, 0.26 mmol) in a Schlenk flask to form a purple slurry. A solution of NaHBEt 3 in Et 2 O (0.065 M, 4 ml, 0.26 mmol) was added dropwise at 238 K to the slurry. The mixture was warmed to room temperature (ca 293 K) for 1 h and evolved to a red slurry. The mixture was filtered and the filtrate was concentrated under vacuum to afford purple crystals of 1, which were identified by X-ray crystallographic analysis.

1-Phenylimido-1-{6-[1-(phenylimino)ethyl]pyridin-2-yl}ethan-1-yl-κ 3 N,N′,N′′)iron(II)
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.