Crystal structure of ruthenocenecarbonitrile

The ruthenocenecarbonitrile molecule exhibits mirror symmetry in the solid state.


Chemical context
The nitrile group is isoelectronic with the acetylid function (Bonniard et al., 2011), which has already been investigated in electron-transfer studies (see, for example, Lang et al., 2006;Poppitz et al., 2014;Speck et al., 2012;Miesel et al., 2013). Coordination of, for example, ferrocenecarbonitrile towards transition metals M will allow investigation of the electronic properties of -C N-M-or -C N-M-N C-bridging units. A synthesis for ferrocenecarbonitrile has already been described in 1957 (Graham et al., 1957); however, only one example of an application in electrochemical studies has been described by Dowling et al. (1981). This prompted us to synthesize ferrocenecarbonitrile transition metal complexes to investigate the electronic properties of the -C N-M-N Cbridging units (Strehler et al. 2013(Strehler et al. , 2014. In a continuation of this work, we present herein the synthesis and crystal structure of the related ruthenocenecarbonitrile, (I). The synthesis of this compound was realized by treatment of formylruthenocene with hydroxylamine hydrochloride, zinc oxide and potassium iodide in acetonitrile, which is similar to a procedure already described for the synthesis of ferrocenecarbonitrile (Kivrak & Zora, 2007).

Structural commentary
The title compound contains one half-molecule in the asymmetric unit with a mirror plane bisecting the molecule through atoms C1, C2, C5, N1 and Ru1 (Fig. 1). The Ru1-centroid distance to the C N-substituted cyclopentadienyl ring is ISSN 2056-9890 slightly increased [1.8179 (1) Å ] compared to the unsubstituted C 5 H 5 unit [1.8157 (1) Å ]. Both cyclopentadienyl rings adopt an ideally eclipsed conformation and are virtually oriented parallel towards each other, which is expressed by the bond angle at the Ru II between the two centroids (= D), with D(C 5 H 4 )-Ru1-D(C 5 H 5 ) = 178.87 (1) . However, the Ru II atom is slightly shifted from the centre of the C 5 ring to the nitrile-bonded C2 atom, which can be explained best by the significantly different Ru-C bond lengths (Table 1) and also the Ru-D-C angles, which should ideally be 90 (Table 1). This is in accordance with the shift in the ferrocenedicarbonitrile structure (Altmannshofer et al., 2008). The C N substituent itself is bent away from the metal atom in (I), with a maximum shift for N1 [0.047 (4) Å ].

Supramolecular features
The packing of (I) consists of a layer-type structure parallel to (010) with the direction of the C N function aligned parallel to [101], alternating between adjacent layers. A further order is observed by a columnar arrangement of slightly tilted molecules parallel to [100]. Weak intermolecularinteractions within the sum of the van der Waals radii (AE = 3.4 Å ; Bondi, 1964) are present between C5 and the C1 0 atom [3.363 (3) Å ] of the overlying molecule in the same layer ( Fig. 2).
[Symmetry code: (A) x, Ày + 1 2 , z.] Table 1 Selected bond lengths (Å ) and angles ( ) for the clarification of the shift of the Ru1 atom towards the C N substituent in (I).
D is the centroid of the C 5 H 4 or C 5 H 5 ring.

Synthesis and crystallization
Formylruthenocene was prepared according to a published procedure (Mueller-Westerhoff et al., 1993). Synthesis of ruthenocenecarbonitrile, (I): formylruthenocene (2.27 g, 8.8 mmol), hydroxylamine hydrochloride (0.96 g, 13.8 mmol), zinc oxide (0.86 g, 10.6 mmol) and potassium iodide (1.76 g, 10.6 mmol) were suspended in 120 ml of dry acetonitrile. The mixture was stirred for 4 h at precisely 368 K. After cooling the reaction mixture to ambient temperature, 18 ml of an aqueous Na 2 S 2 O 3 (5%) solution were added in a single portion, and stirring was continued for additional 20 min. Solid particles were removed by filtration and the filtrate was extracted with ethyl acetate (3 Â 50 ml). The combined organic layers were dried over MgSO 4 . All volatiles were removed under reduced pressure and the crude product was purified by flash chromatography on aluminum oxide using dichloromethane as eluent. Greenish crystals of (I) were obtained by slow evaporation of a saturated dichloromethane solution containing (I) at ambient temperature (yield: 820 mg

Ruthenocenecarbonitrile
Crystal data