Tricarbonyl(η6-4′,7-dimethoxyisoflavone)chromium(0)

The metal atom of the Cr(CO)3 unit of the title compound, [Cr(C17H14O4)(CO)3], is coordinated to the methoxyphenyl ring of the isoflavone ligand; the Cr(CO)3 unit exhibits a three-legged piano-stool conformation. The aromatic ring of the methoxyphenyl group is twisted by 42.49 (9)° with respect to the γ-pyrone ring. In the fused-ring, the dihedral angle between the phenylene and γ-pyrone rings is 3.08 (13)°.

The metal atom of the Cr(CO) 3 unit of the title compound, [Cr(C 17 H 14 O 4 )(CO) 3 ], is coordinated to the methoxyphenyl ring of the isoflavone ligand; the Cr(CO) 3 unit exhibits a threelegged piano-stool conformation. The aromatic ring of the methoxyphenyl group is twisted by 42.49 (9) with respect to the -pyrone ring. In the fused-ring, the dihedral angle between the phenylene and -pyrone rings is 3.08 (13) .

Experimental
Crystal data [Cr(C 17  Financial assistance from the University of the Free State and SASOL to JHvT is gratefully acknowledged. We would like to express our gratitude to the School of Chemistry at the University of the Witwatersrand for the use of the diffractometer. Special thanks are due to Dr M. A. Fernandes. Opinions, findings, conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of SASOL. The longest Cr-C(arene) bond is Cr-C4', that in turn is bonded to the O4'-C41' methoxy group. This bond elongation is probably due to the methoxy group that weakens the π-interaction ability of C4' towards the chromium metal centre. These distances are within the normal range, see Allen (2002). The phenyl ring is essentialy planar (r.m.s of fitted atoms C1'-C6' = 0.0119 Å). Slight molecular disorder is displayed by a twist in the isoflavone backbone, that forms a dihedral angle of 42.49 (9)° between the phenyl and γ-pyrone ring and a dihedral angle of 41.1 (1)° between the phenyl and the benzopyrone ring system. A dihedral angle of 3.08 (13)° is also present between the benzene and the γ-pyrone ring, with a r.m.s of fitted atoms C2-C10 and O5 of 0.0387 Å. The O4'-C41' methoxy group on the phenyl ring bends towards the Cr(CO) 3 moiety, forming the C5'-C4'-O4'-C41' tortion angle of 15.9 (4)°. The O7-C71 methoxy group on the benzene ring is also slightly displaced from the benzene ring plane, shown by the C8-C7-O7-C71 tortion angle of 175.0 (3)°.
Other molecular geometrical parameters is in good agreement with literature values, see Allen (2002). Selected geometrical parameters is presented in Table 1.
As illustrated in Fig.2 the molecular packing is such that a benzene ring of one molecule is above the γ-pyrone ring of a neighbouring molecule, separated by a plane to plane distance of 3.369 Å and a centroid to centroid distance of 4.281 Å.

Refinement
The H atoms were positioned geometrically and refined using a riding model with fixed C-H distances of 0.93 Å (CH) [U iso (H) = 1.2U eq ] and 0.96 Å (CH 3 ) [U iso (H) = 1.5U eq ] respectively. Initial positions of methyl H-atoms were obtained from fourier difference and refined as a fixed rotor.

Special details
Experimental. The intensity data was collected on a Bruker Apex II CCD diffractometer using an exposure time of 10 s/frame. The 509 frames were collected with a frame width of 0.5° covering up to θ = 28° with 99.4% completeness accomplished.
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.