Ferrocenylbutadiyne

The title compound, [Fe(C5H5)(C9H5)], crystallizes in a form of a π–π-stacked assembly formed as a result of strong intermolecular π–π interactions between (a) the triple bonds of two neighboring butadiyne substituents overlapping in a ‘head-to-tail’ fashion [characterized by C⋯C short contacts of 3.622 (5), 3.567 (6) and 3.556 (6) Å] and (b) the triple bonds of the butadiyne substituent and substituted cyclopendadiene ring of neighboring molecules [C⋯C = 3.474 (5) and 3.492 (6) Å]. The linear butadiyne substituent has alternating C—C triple and single bonds, while the unsubstituted cyclopentadiene ring is slightly positionally disordered (although the structure reported here was solved as non-disordered) and retains a close to eclipsed conformation.


Experimental
Crystal data [Fe(C 5
Finantial support from the National Science Foundation (grant CHE-0809203) is greatly appreciated. The X-ray data were collected at the University of Minnesota Duluth X-ray crystallography facility.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HG2474).
There are a number of known structures of substituted ferrocenes (Stepnika, 2008, Nemykin et al., 2007a, 2007c but this is the first reported crystal structure of a butadiyne substituted ferrocene. The molecule crystallizes as a π-π stacked assembly in the centrosymmetric monoclinic space group P2 1 /c . π-π stacked assembly formed as a result of strong intermolecular π-π interactions between (a) the triple bonds of two butadiyne substituents in molecules 'B' and 'C' (Figure 2) overlapping in 'head-to-tail' fashion and (b) the triple bonds of butadiyne substituents of a substituted cyclopendadiene ring along crystallographic b axis ( Figure 2). Intermolecular π-π interactions between between the triple bonds of two butadiyne substituents (overlapping in 'head-to-tail' fashion) consists of three short contacts between C12 and C14 (3.622 (5) Å, -x, 1 -y, 1 -z), C13 and C14 (3.567 (6) Å, -x, 1 -y, 1 -z), and C13 and C13 (3.556 (6) Å, -x, 1 -y, 1 -z) carbon atoms of neighboring molecules. Intermolecular π-π interactions between between the triple bonds of butadiyne substituents and substituted cyclopentadiene ring of neighboring molecule can be characterized by two short contacts between C2 and C11 (3.474 (5) Å, -x, -y, 1 -z) and C3 and C12 (3.492 (6) Å, -x, -y, 1 -z) pairs of carbon atoms. The terminal H15 atom of the butadiyne substituent of one molecule is in close proximity to the H6 atom on the unsubstituted cyclopentadienyl ring of the other molecule. Although the unsubstituted cyclopentadiyne ring is, probably, disordered over two crystallographical positions (with disordered structure solution available from the authors on request), the unsubstituted cyclopentadiene ring retains close to eclipsed conformation of ferrocene subunit. In addition, the butadiyne substituent has alternating C-C triple and single bonds.

Experimental
The title compound was obtained as by-product of the iodination reaction of ferrocenylacetylene (Nemykin et al., 2007c).

Refinement
All cyclopentadienyl H atoms positioned geometrically, while the terminal butadiyne H atom was located on a Fourier map. The H atoms were initially refined with soft restraints on the bond lengths and angles to regularize their geometry (C(Ferrocene) -H 0.93; ≡C-H 0.82 Å) and U iso (H) (in the range 1.2-1.5 times U eq of the parent atom) using default supplementary materials sup-2 procedure available in Crystals for Windows software (Betteridge et al., 2003). After this the positions were refined with riding constraints.
The difference between the number of independent reflections (2411) and those included in the refinement (2402) is originate from the filter used by Crystals for Windows software. The filter uses (sin theta/lambda) 2 at least 0.0100 cutoff in order to eliminate reflections that may be poorly measured in the vicinity of the beam stop. Fig. 1. The title compound with displacement ellipsoids drawn at the 50% probability level. H atoms are shown as spheres of arbitary radius. Fig. 2. Intermolecular π-π interactions in the title compound. displacement ellipsoids drawn at the 50% probability level. Molecules located at: 1 -x, 3/2 + y, 3/2 -z (molecule A); 1 + x, 3/ 2 -y, 1/2 + z (molecule B); 1 -x, 1/2 + y, 3/2 -z (molecule C); and 1 + x, 1/2 -y, 1/2 + z (molecule D).